Washington (CNN) CIA Director Mike Pompeo did meet with the head of Russia's foreign intelligence agency, an official barred from entering the US under 2014 sanctions, as well as the head of Russia's internal security agency, according to a US official with direct knowledge of the meetings.

The official said Pompeo did not meet with the head of the GRU, the Russian military intelligence agency behind efforts to meddle in the 2016 US election. The CIA followed a multi-agency legal process to give access to Russian officials under sanctions, the official said.

CIA Director Mike Pompeo defended the meeting in a Thursday letter to Senate Minority Leader Chuck Schumer, declaring that he and other officials met with Russians for the same reason their predecessors did -- "to keep Americans safe."

Schumer, whose staff was briefed on the meetings and the legal process involved before giving a Tuesday news conference, said the meeting represented "a serious national security issue." And he continued to blast Pompeo on Thursday.

"If this administration is ignoring sanctions, that's very serious," the New York Democrat told CNN, noting that in the letter, Pompeo didn't directly acknowledge that he had met with his Russian counterparts. "Director Pompeo's refusal to answer that question is deeply troubling."

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