Washington (CNN) Democratic Sen. Jeff Merkley said Monday that he asked the FBI to open a perjury investigation into Homeland Security Secretary Kirstjen Nielsen last week because "it's time for some real accountability."

"I am just sick and tired of this administration lying to the American people, lying to Congress, doing it under oath," he told CNN's John Berman on "New Day."

On Friday, Merkley asked the FBI to investigate Nielsen a day after he released a draft memo that shows the Trump administration was drafting policy to separate families apprehended at the US-Mexico border as early as December 2017. Both the administration and Nielsen repeatedly have said there was no policy to separate families. Merkley said Nielsen made the same claim when she testified before Congress last month.

"I write to request an investigation to determine whether Secretary of Homeland Security Kirstjen Nielsen committed perjury during her sworn testimony before the House Committee on the Judiciary on December 20, 2018," Merkley wrote in his request to FBI Director Christopher Wray. "Compelling new evidence has emerged revealing that high-level Department of Homeland Security officials were secretly and actively developing a new policy and legal framework for separating families as far back as December 2017."

Merkley noted Monday that the FBI has not yet responded to his request, but said that "this is the official, right way to initiate a referral to the FBI for pursuit of an investigation regarding perjury."

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