0603 GMT October 19, 2017
During a meeting at the White House last week, the president shared classified information with Russian Foreign Minister Sergey Lavrov and Russia's ambassador to the US, Sergey Kislyak, The Washington Post claimed in a report.
McMaster appeared before reporters on Monday to deny the report, asserting that it "is false" and "at no time were any intelligence sources or methods discussed."
"I was in the room. it didn't happen," said the American general.
Earlier, US Secretary of State Rex Tillerson said Trump discussed "the nature of specific threats" during the meeting, "but they did not discuss sources, methods or military operations."
According to Deputy National Security Adviser Dina Powell "This story is false" as Trump "only discussed the common threats that both countries faced."
In its report, the Post cited unnamed current and former officials as making the claim.
The chairman of the Senate Foreign Relations Committee, Republican Senator Bob Corker, also reacted to the report, noting that the White House "has got to do something soon to bring itself under control and order."
"Obviously they're in a downward spiral right now and they've got to figure out a way to come to grips with all that's happening," said the Tennessee lawmaker. "The chaos that is being created by the lack of discipline — it's creating an environment that I think makes — it creates a worrisome environment."
Trump reportedly offered details about a Daesh terror threat related to the use of laptop computers on aircraft.
The sensitive information was said to have been provided by a US ally, and revealing it could jeopardize the United States, the newspaper said, adding that the CIA was unwilling to comment on the matter.
Trump has been under investigation over possible collusion with the Kremlin during the 2016 presidential campaign and transition.