Donald Trump has defended his sharing of information with Russian officials, saying he has an "absolute right" to do so as president.
He tweeted that he wanted to share with Russia "facts pertaining to terrorism and airline flight safety".
His Twitter post added: "Humanitarian reasons, plus I want Russia to greatly step up their fight against ISIS & terrorism."
As President I wanted to share with Russia (at an openly scheduled W.H. meeting) which I have the absolute right to do, facts pertaining....— Donald J. Trump (@realDonaldTrump) May 16, 2017
...to terrorism and airline flight safety. Humanitarian reasons, plus I want Russia to greatly step up their fight against ISIS & terrorism.— Donald J. Trump (@realDonaldTrump) May 16, 2017
Mr Trump's response came after the Washington Post reported that he revealed highly classified information to senior Russian officials during an Oval Office meeting last week, putting a source of intelligence on the Islamic State group at risk.
The disclosure drew strong condemnation from Democrats and a rare rebuke of the president from some Republican legislators.
White House officials denounced the report, saying the president did not disclose intelligence sources or methods to the Russians, although officials did not deny that classified information was disclosed in the May 10 meeting.
"The president and the foreign minister reviewed a range of common threats to our two countries including threats to civil aviation," said HR McMaster, Mr Trump's national security adviser.
"At no time were intelligence sources or methods discussed and the president did not disclose any military operations that were not already publicly known."
The Post, citing current and former US officials, said Mr Trump shared details about an IS threat related to the use of laptops on aircraft with Russian foreign minister Sergei Lavrov and ambassador to the US Sergey Kislyak.
The ambassador has been a central player in the controversy surrounding possible co-ordination between Mr Trump's campaign and Moscow's election meddling.
The officials said the information Mr Trump relayed during the Oval Office meeting had been provided by a US partner through an intelligence-sharing arrangement. They said it was considered so sensitive that details have been withheld from allies and tightly restricted even within the US government.
The New York Times and BuzzFeed News published similar reports later on Monday.
Maria Zakharova, a spokeswoman for the Russian foreign ministry, described the reports as "yet another fake".
The revelations could further damage Mr Trump's already fraught relationship with US intelligence agencies. He has openly questioned the competency of intelligence officials and challenged their high-confidence assessment that Russia meddled in last year's presidential election to help him win.
His criticism has been followed by a steady stream of leaks to the media that have been damaging to him and exposed an FBI investigation into his associates' possible ties to Russia.
The disclosure also risks harming his credibility with US partners around the world ahead of his first overseas trip. The White House was already reeling from its botched handling of his decision last week to fire James Comey, the FBI director who was overseeing the Russia investigation.
I have been asking Director Comey & others, from the beginning of my administration, to find the LEAKERS in the intelligence community.....— Donald J. Trump (@realDonaldTrump) May 16, 2017
A European security official said sharing sensitive information could dampen the trust between the US and its intelligence-sharing partners.
"It wouldn't likely stop partners from sharing life-saving intelligence with the Americans, but it could impact the trust that has been built, particularly if sharing such information exposes specific intelligence-gathering methods," said the official.
Secretary of state Rex Tillerson also disputed the Post report. He said Mr Trump discussed a range of subjects with the Russians, including "common efforts and threats regarding counter-terrorism". The nature of specific threats was discussed, he said, but not sources, methods or military operations.
The Post said the intelligence partner had not given the US permission to share the material with Russian officials. By doing so, Mr Trump would have jeopardised co-operation from an ally familiar with the inner workings of IS, and make other allies - or even US intelligence officials - wary about sharing top secret details with the president.