U.S. Defense Secretary Jim Mattis said he had no concerns about the Trump administration's handling of classified information and added the issue had not come up in his talks on Tuesday with several U.S. allies, saying: "No, I'm not worried."

But at the same time, Mattis deferred to the White House and acknowledged he knew little more about the uproar than what he had "read in the newspaper."

U.S. officials, speaking on condition of anonymity, have previously said Trump discussed intelligence about Islamic State with Russian Foreign Minister Sergei Lavrov and Russian Ambassador Sergei Kislyak at last Wednesday's talks in the Oval Office.