(CBS News) -- President Donald Trump revealed "highly classified" intelligence to Russian Foreign Minister Sergey Lavrov and Ambassador Sergey Kislyak during a meeting at the White House last week, according to The Washington Post.
The disclosures may have endangered a key intelligence source involved with the campaign against the Islamic State of Iraq and Syria (ISIS), U.S. officials told the paper.
The information shared by Mr. Trump with the Russians was not collected by U.S. intelligence. Rather, it was given to the U.S. by an ally in the fight against ISIS, and was provided with the understanding that it would not be shared with other countries without permission.
The intelligence was "code-word information," the Post reports. That's the term used for intelligence classified at the highest possible level. U.S. officials worry that the disclosure of the information will do serious harm to relations with the ally in question.
"If that partner learned we'd given this to Russia without their knowledge or asking first that is a blow to that relationship," a U.S. official told the Post.
A source familiar with the workings of the Senate Intelligence Committee says the committee members -- including its leaders -- have not been briefed on the president's alleged comments to the Russians, according to CBS News' Nancy Cordes.
One official told the paper that Mr. Trump "revealed more information to the Russian ambassador than we have shared with our own allies." But given the president's wide latitude in declassifying materials, it's unlikely that he broke any laws by sharing the information with the Russians.
Secretary of State Rex Tillerson issued a statement following the report's publication. "During President Trump's meeting with Foreign Minister Lavrov, a broad range of subjects were discussed among which were common efforts and threats regarding counter-terrorism," said Tillerson. "During that exchange the nature of specific threats were discussed, but they did not discuss sources, methods or military operations."
"The president and the foreign minister reviewed common threats from terrorist organizations to include threats to aviation," National Security Advisor Gen. H.R. McMaster, a participant in the president's meeting with the Russian officials, told the paper. "At no time were any intelligence sources or methods discussed and no military operations were disclosed that were not already known publicly."
Confronted by reporters outside the West Wing on Monday shortly after the Post's report was published, McMaster said, "This is the last place in the world I wanted to be. I'm leaving."
Later Monday, McMaster read a similar statement to reporters gathered outside the White House. "The story that came out tonight, as reported, is false," said McMaster, who took no questions. "At no time, at no time, were intelligence sources or methods discussed. And the president did not disclose any military operations that were not already publicly known. Two other senior officials who were present, including the secretary of state, remember the meeting the same way and have said so. Their on-the-record accounts should outweigh those from anonymous sources. I was in the room. It didn't happen."
However, the Post report doesn't say that Mr. Trump discussed methods or sources with Lavrov and Kislyak. Instead, the paper says Mr. Trump discussed information provided by a source relating to a specific terrorist threat. In doing so, he disclosed elements of a plot being planned by ISIS, the danger posed by the plot, and the city in ISIS-held territory where the U.S. ally had detected the threat.
Based on that information, "Russia could identify our sources or techniques," a senior U.S. official told the Post, although the response from Lavrov and Kislyak at the time was reportedly "muted."
Mr. Trump is reported to have boasted that he had access to classified information during his meeting with the Russians.
"I get great intel. I have people brief me on great intel every day," the Post reported Mr. Trump as saying, citing a U.S. official.