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The Trump administration was drafting policy to separate families apprehended at the US-Mexico border as early as December 2017, according to a draft memo released Thursday night, despite later claims that no such policy existed.

Sen. Jeff Merkley released a 2017 memo drafted by senior officials in the Department of Homeland Security and the Department of Justice detailing the plans.

“This memo really nails down the lies the administration was telling the public,” the Oregon Democrat told CNN. “The secretary of homeland security said that they did not have a policy of child separation. Well, this memo shows that there was a high-level discussion planning for that.”

He added: “The big picture here is while the President is talking about a crisis on the border – from rapists and murderers flooding into America – the administration is talking internally about families applying for asylum and developing a strategy to deter them by the US government inflicting trauma on children.”

Responding to the release of the memo, DHS spokeswoman Katie Waldman said, “The Trump administration has made clear that all legal options are on the table to enforce the rule of law, rein in mass unchecked illegal immigration, and defend our borders.” Waldman cited an increase in apprehensions in December 2017 as reason for the concern.

“It would be malpractice to not seriously examine every single avenue to gain operational control of the border and ensure that those who are entering our country have a legal right to be here,” she added.

The draft memo, which Merkley said he had received via a government whistleblower, provides a snapshot of the extent the administration was willing to go to deter migrants from trekking to the US-Mexico border, ranging from separating families to possibly denying children asylum hearings. It was previously reported by NBC News.

The draft, dated December 2017, includes plans to separate families months before the “zero-tolerance” immigration policy was announced by then-Attorney General Jeff Sessions. Under a section dubbed “short term (next 30 days) options,” the memo says: “Separate Family Units. Announce that DHS is considering separating family units, placing the adults in adult detention and placing the minors under the age of 18 in the custody of HHS as unaccompanied alien children. …”

It goes on to note that advocacy groups were aware of the possible changes and preparing to “bring a class action lawsuit.” As a result, “close coordination with DOJ will also be required.” The intent of prosecuting parents, as stated in the memo: “the increase in prosecutions would be reported by the media and it would have substantial deterrent effect.”

The draft memo comes amid a partial government shutdown over President Donald Trump’s border wall and a new inspector general report revealing that the number of children separated from a parent or guardian last year far surpassed previously reported figures.

This story has been updated.

CNN’s Geneva Sands contributed to this report.