State Department warns Americans about European travel | CNN Politics

People flee the scene of a terror attack at Istanbul's Ataturk airport on June 29. Turkish officials have strong evidence that ISIS leadership was involved in the planning of the attack, a senior government source told CNN. Officials believe the men -- identified by state media as being from Russia, Uzbekistan and Kyrgyzstan -- entered Turkey from the ISIS stronghold of Raqqa in Syria, bringing with them the suicide vests and bombs used in the attack, the source said.

Defne Karadeniz/Getty Images

The ISIS militant group -- led by Abu Bakr al-Baghdadi, pictured -- began as a splinter group of al Qaeda. <a href="http://www.cnn.com/2014/06/29/world/meast/iraq-developments-roundup/" target="_blank">Its aim is to create an Islamic state,</a> or caliphate, across Iraq and Syria. It is implementing Sharia law, rooted in eighth-century Islam, to establish a society that mirrors the region's ancient past. It is known for killing dozens of people at a time and carrying out public executions.

The ISIS militant group -- led by Abu Bakr al-Baghdadi, pictured -- began as a splinter group of al Qaeda. Its aim is to create an Islamic state, or caliphate, across Iraq and Syria. It is implementing Sharia law, rooted in eighth-century Islam, to establish a society that mirrors the region's ancient past. It is known for killing dozens of people at a time and carrying out public executions.

Al-Furqan Media/Anadolu Agency/Getty Images

Kurdish Peshmerga fighters fire missiles during clashes with ISIS in Jalawla, Iraq, on June 14, 2014. That month, ISIS took control of Mosul and Tikrit, two major cities in northern Iraq.

RICK FINDLER/AFP/Getty Images

Traffic from Mosul lines up at a checkpoint in Kalak, Iraq, on June 14, 2014. Thousands of people <a href="http://www.cnn.com/2014/07/19/world/meast/christians-flee-mosul-iraq/" target="_blank">fled Mosul</a> after it was overrun by ISIS.

Traffic from Mosul lines up at a checkpoint in Kalak, Iraq, on June 14, 2014. Thousands of people fled Mosul after it was overrun by ISIS.

Dan Kitwood/Getty Images

ISIS fighters parade down an Iraqi street in this image released by the group in July 2014.

ISIS

Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and other Yazidi people are flown to safety after a <a href="http://www.cnn.com/2014/08/11/world/gallery/kurdistan-rescue-mission-mount-sinjar/index.html">dramatic rescue operation</a> at Iraq's Mount Sinjar on August 11, 2014. A CNN crew <a href="http://www.cnn.com/2014/08/11/world/meast/iraq-rescue-mission/index.html">was on the flight,</a> which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. Only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and other Yazidi people are flown to safety after a dramatic rescue operation at Iraq's Mount Sinjar on August 11, 2014. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. Only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

Warzer Jaff/CNN

On August 19, 2014, American journalist James Foley <a href="http://www.cnn.com/2014/08/19/world/meast/isis-james-foley/" target="_blank">was decapitated by ISIS militants </a>in a video posted on YouTube. A month later, they released videos showing the executions of American journalist Steven Sotloff and British aid worker David Haines.

On August 19, 2014, American journalist James Foley was decapitated by ISIS militants in a video posted on YouTube. A month later, they released videos showing the executions of American journalist Steven Sotloff and British aid worker David Haines.

NICOLE TUNG/AFP/Getty Images

ISIS militants stand near the site of an airstrike near the Turkey-Syria border on October 23, 2014. The United States and several Arab nations <a href="http://www.cnn.com/2014/09/22/world/meast/u-s-airstrikes-isis-syria/" target="_blank">began bombing ISIS targets in Syria</a> to take out the group's ability to command, train and resupply its fighters.

ISIS militants stand near the site of an airstrike near the Turkey-Syria border on October 23, 2014. The United States and several Arab nations began bombing ISIS targets in Syria to take out the group's ability to command, train and resupply its fighters.

BULENT KILIC/AFP/Getty Images

A Kurdish marksman stands atop a building as he looks at the destroyed Syrian town of Kobani on January 30, 2015. After four months of fighting, Peshmerga forces liberated the city from the grip of ISIS.

BULENT KILIC/AFP/Getty Images

Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on February 4, 2015. Al-Kasasbeh's son, <a href="http://www.cnn.com/2015/02/03/world/gallery/jordanian-pilot-reaction/index.html" target="_blank">Jordanian pilot Moath al-Kasasbeh,</a> was burned alive in a video that was released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on February 4, 2015. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

Nasser Nasser/AP

In February 2015, British newspapers report the identity of "Jihadi John," the disguised man with a British accent who had appeared in ISIS videos executing Western hostages. The militant was identified as Mohammed Emwazi, a Kuwaiti-born Londoner. On November 12, 2015, the Pentagon announced that Emwazi was in a vehicle hit by a drone strike. ISIS later confirmed his death.

DANIEL SORABJI/AFP/Getty Images

In March 2015, ISIS released video and images of a man being thrown off a rooftop in Raqqa, Syria. In the last photograph, the man is seen face down, surrounded by a small crowd of men carrying weapons and rocks. The caption reads "stoned to death." The victim was brutally killed because he was accused of being gay.

ISIS

An Iraqi soldier searches for ISIS fighters in Tikrit on March 30, 2015. Iraqi forces retook the city after it had been in ISIS control since June 2014.

Khalid Mohammed/AP

In May 2015, ISIS took control of Palmyra, Syria, and <a href="http://www.cnn.com/2015/05/15/middleeast/gallery/palmyra-ruins-syria/index.html" target="_blank">began to destroy ancient ruins and artifacts.</a> The Temple of Bel is seen here after Syrian forces reclaimed the city in March 2016. ISIS has also <a href="http://www.cnn.com/2015/03/09/world/iraq-isis-heritage/" target="_blank">destroyed other cultural sites</a> in Syria and Iraq.

In May 2015, ISIS took control of Palmyra, Syria, and began to destroy ancient ruins and artifacts. The Temple of Bel is seen here after Syrian forces reclaimed the city in March 2016. ISIS has also destroyed other cultural sites in Syria and Iraq.

JOSEPH EID/AFP/Getty Images

Dead bodies lie near a beachside hotel in Sousse, Tunisia, after <a href="http://www.cnn.com/2015/06/26/world/gallery/tunisia-terrorist-attack/index.html" target="_blank">a gunman opened fire</a> on June 26, 2015. ISIS claimed responsibility for the attack, which killed at least 38 people and wounded at least 36 others, many of them Western tourists. Two U.S. officials said they believed the attack might have been inspired by ISIS but not directed by it.

Dead bodies lie near a beachside hotel in Sousse, Tunisia, after a gunman opened fire on June 26, 2015. ISIS claimed responsibility for the attack, which killed at least 38 people and wounded at least 36 others, many of them Western tourists. Two U.S. officials said they believed the attack might have been inspired by ISIS but not directed by it.

Jawhara FM via AP

ISIS also claimed responsibility for what it called a suicide bombing <a href="http://www.cnn.com/2015/06/26/world/kuwait-mosque-attack/" target="_blank">at the Al-Sadiq mosque</a> in Kuwait City on June 26, 2015. At least 27 people were killed and at least 227 were wounded, state media reported at the time. The bombing came on the same day as the attack on the Tunisian beach.

ISIS also claimed responsibility for what it called a suicide bombing at the Al-Sadiq mosque in Kuwait City on June 26, 2015. At least 27 people were killed and at least 227 were wounded, state media reported at the time. The bombing came on the same day as the attack on the Tunisian beach.

YASSER AL-ZAYYAT/AFP/Getty Images

A man inspects the aftermath of a car bombing in Khan Bani Saad, Iraq, on July 18, 2015. <a href="http://www.cnn.com/2015/07/18/middleeast/iraq-violence/" target="_blank">A suicide bomber with an ice truck,</a> promising cheap relief from the scorching summer heat, lured more than 100 people to their deaths. ISIS claimed responsibility on Twitter.

A man inspects the aftermath of a car bombing in Khan Bani Saad, Iraq, on July 18, 2015. A suicide bomber with an ice truck, promising cheap relief from the scorching summer heat, lured more than 100 people to their deaths. ISIS claimed responsibility on Twitter.

Karim Kadim/AP

Two women hold hands after an explosion in Suruc, Turkey, on July 20, 2015. The blast <a href="http://www.cnn.com/2015/07/22/world/turkey-suruc-explosion/index.html" target="_blank">occurred at the Amara Cultural Park,</a> where a group was calling for help to rebuild the Syrian city of Kobani, CNN Turk reported. At least 32 people were killed and at least 100 were wounded in the bombing. Turkish authorities said they believed ISIS was involved in the explosion.

Two women hold hands after an explosion in Suruc, Turkey, on July 20, 2015. The blast occurred at the Amara Cultural Park, where a group was calling for help to rebuild the Syrian city of Kobani, CNN Turk reported. At least 32 people were killed and at least 100 were wounded in the bombing. Turkish authorities said they believed ISIS was involved in the explosion.

DEPO PHOTOS/AFP/Getty Images

Spectators at the Stade de France in Paris run onto the soccer field after explosions were heard outside the stadium on November 13, 2015. Three teams of gun-wielding ISIS militants hit six locations around the city, killing at least 129 people and wounding hundreds.

Christophe Ena/AP

Law enforcement officers search a residential area in San Bernardino, California, after a <a href="http://www.cnn.com/2015/12/02/us/gallery/san-bernardino-shooting/index.html" target="_blank">mass shooting</a> killed at least 14 people and injured 21 on December 2, 2015. <a href="http://www.cnn.com/2015/12/03/us/san-bernardino-shooting/index.html" target="_blank">The shooters</a> -- Syed Rizwan Farook and his wife, Tashfeen Malik -- were fatally shot in a gunbattle with police hours after the initial incident. The couple supported ISIS and had been planning the attack for some time, investigators said.

Law enforcement officers search a residential area in San Bernardino, California, after a mass shooting killed at least 14 people and injured 21 on December 2, 2015. The shooters -- Syed Rizwan Farook and his wife, Tashfeen Malik -- were fatally shot in a gunbattle with police hours after the initial incident. The couple supported ISIS and had been planning the attack for some time, investigators said.

PATRICK T. FALLON/AFP/Getty Images

Members of Iraq's elite counterterrorism unit celebrate December 28, 2015, after <a href="http://www.cnn.com/2015/12/28/middleeast/iraq-military-retakes-ramadi/" target="_blank">recapturing the city of Ramadi.</a> The city fell to ISIS in May 2015.

Members of Iraq's elite counterterrorism unit celebrate December 28, 2015, after recapturing the city of Ramadi. The city fell to ISIS in May 2015.

AHMAD AL-RUBAYE/AFP/Getty Images

Two wounded women sit in the airport in Brussels, Belgium, after two explosions rocked the facility on March 22, 2016. A subway station in the city <a href="http://www.cnn.com/2016/03/24/europe/brussels-investigation/index.html" target="_blank">was also targeted in terrorist attacks</a> that killed at least 30 people and injured hundreds more. Investigators say the suspects belonged to the same ISIS network that was behind the Paris terror attacks in November.

Two wounded women sit in the airport in Brussels, Belgium, after two explosions rocked the facility on March 22, 2016. A subway station in the city was also targeted in terrorist attacks that killed at least 30 people and injured hundreds more. Investigators say the suspects belonged to the same ISIS network that was behind the Paris terror attacks in November.

KETEVAN KARDAVA/Georgian Public Broadcaster/AFP/Getty Images

A boy walks past bloodstains and debris at a cafe in Balad, Iraq, that was attacked by ISIS gunmen on May 13, 2016. Twenty people were killed.

AHMAD AL-RUBAYE/AFP/Getty Images

Iraqi government forces patrol in southern Falluja, Iraq, on June 10, 2016. In late June, <a href="http://www.cnn.com/2016/06/26/middleeast/falluja-liberated-isis/index.html" target="_blank">a senior Iraqi general announced</a> that the battle to reclaim Falluja from ISIS had been won.

Iraqi government forces patrol in southern Falluja, Iraq, on June 10, 2016. In late June, a senior Iraqi general announced that the battle to reclaim Falluja from ISIS had been won.

AHMAD AL-RUBAYE/AFP/Getty Images

The ISIS terror threat

Story highlights

The State Department is warning Americans of the risk of potential terrorist attacks throughout Europe

Concerns are particularly high over a soccer tournament in France next month

Washington CNN —

The State Department is warning Americans about the risk of potential terrorist attacks throughout Europe as law enforcement waits on heightened alert for possible ISIS-inspired attacks.

The department on Tuesday issued a travel alert for the continent. There isn’t a new, specific threat, but the warning comes ahead of big events this summer with large crowds. Venues in France will host the European Soccer Championship beginning on June 10, and the Catholic Church’s World Youth Day will be held in Krakow, Poland.

Both events are expected to draw massive crowds, and concerns are particularly high over the soccer tournament.

“Euro Cup stadiums, fan zones, and unaffiliated entertainment venues broadcasting the tournaments in France and across Europe represent potential targets for terrorists, as do other large-scale sporting events and public gathering places throughout Europe,” the new State Department alert reads.

The travel alert, which expires on August 31, follows increased worry after two large terrorist attacks in Europe, first in Paris and then two months ago in Brussels, Belgium.

The United States has for some time warned U.S. citizens to stay vigilant in crowded settings abroad. But U.S. intelligence and counterterrorism officials believe Europe is in for a summer similar to last year’s in the United States.

The FBI increased 24/7 surveillance of jihadist suspects and made more than a dozen arrests. In some cases, suspects were arrested on non-terror related charges simply to get them off the streets and out of fear it wasn’t safe to wait to gather terror-related evidence.

A French intelligence official told CNN recently that authorities don’t believe they’ve arrested all members of an extended cell behind the recent attacks in Paris and Brussels. While they know more about the cell and have identified more people serving as supporting role, the threat hasn’t waned, the official said.