WASHINGTON — The Trump administration hunkered down Monday evening following reports that President Donald Trump revealed highly classified information about the Islamic State during an already controversial Oval Office visit with Russia’s foreign minister and its ambassador to the United States.

Top Cabinet-level officials tried to contain the damage caused by the report, but their efforts were overwhelmed by questions about White House credibility, including discredited statements about the firing of FBI Director James Comey.

Congressional Democrats were quick to demand an investigation into what Trump told the visiting Russian officials. Republicans were more circumspect, but also expressed concern about the report.

“I have no idea if it’s true. If it is, it would be very troubling,” Sen Lindsey Graham, R-S.C., a member of the Senate Intelligence Committee, said in an emailed response to a question.

“The importance of carefully handling classified information was one of the big lessons of 2016,” said Rep. Carlos Curbelo, R-Fla. “All leaders should be held to same standard.”

The Washington Post touched off the controversy by reporting that Trump had disclosed intelligence to Foreign Minister Sergey Lavrov and Ambassador Sergey Kislyak during their meeting with Trump last week. According to the Post, the information had been provided by an American ally through a sensitive intelligence-sharing arrangement. A U.S. official familiar with the issue said Trump “revealed more information to the Russian ambassador than we have shared with our own allies.”

What was specifically revealed is murky, but the Post reported that the U.S. partner had not given permission for the information to be shared with Russia, a major breach of intelligence protocol. After the meeting, White House officials reportedly reached out to the CIA and the National Security Agency to explain what happened.

National security adviser H.R. McMaster told reporters gathered outside the White House that the report was false, but the wording of his denial addressed an aspect of the situation that the Post story had not, leaving in doubt whether the information itself had been revealed.

“At no time were intelligence sources or methods discussed,” McMaster said. “I was in the room, it didn’t happen.” He offered no further comment and did not take questions.

Secretary of State Rex Tillerson offered a denial that seemed to suggest some information had been shared. He said the meeting with the foreign minister covered a broad range of subjects, including terrorism threats.

“During that exchange the nature of specific threats was discussed, but they did not discuss sources, methods or military operations,” he said.

The new controversy came even as there was no letup in the conflict Trump stirred last week with the firing of Comey and as Trump prepares for his first foreign trip, which includes stops in Saudi Arabia and Israel. On Tuesday, he’s to meet with the president of Turkey, whose relationship with Russia has been warming even as U.S. relations turn frosty over the battle against the Islamic State.

Sen. Mark Warner of Virginia, the senior Democrat on the Senate Select Committee on Intelligence, which is investigating Russia meddling in last year’s election, flayed Trump over the report on Twitter.

“If true, this is slap in the face to the intel community,” he tweeted. “Risking sources & methods is inexcusable, particularly with the Russians.”

Rep. Eliot Engel, D-N.Y., the ranking Democrat on the House Foreign Relations Committee, said he will call McMaster to a classified briefing to find out what specifically was revealed.

“This certainly raises questions about whether the president recognizes the serious implications of disclosing such sensitive information to an adversary,” Engel said.

While Washington shook, Republicans addressed the issue carefully.

“We have no way to know what was said, but protecting our nation’s secrets is paramount. The speaker hopes for a full explanation of the facts from the administration,” said Doug Andres, spokesman for Speaker Paul Ryan, R-Wis.

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(Matthew Schofield, Lesley Clark and Lindsay Wise contributed to this article.)