US President Donald Trump has defended his "absolute right" to discuss sensitive material on terrorism and airline safety at a meeting with Russia's foreign minister.
US media reports said Mr Trump had shared top secret material with Russia's Foreign Minister and ambassador on 10 May.
It related to a plot by the Islamic State group, thought to be centred on the use of laptop computers on aircraft, and came from a partner which had not given permission for it to be shared, the reports said.
The Washington Post reported that others at the meeting realised the mistake and scrambled to "contain the damage" by informing the CIA and NSA.
Defending himself against the claims, Mr Trump tweeted: "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 to terrorism and airline flight safety.
"Humanitarian reasons, plus I want Russia to greatly step up their fight against [IS] & terrorism."
It is not clear if Mr Trump was acknowledging having shared intelligence secrets with the Russian officials, thus contradicting White House statements, or whether he was simply trying to explain what had been discussed.
Mr Trump's alleged disclosures are not illegal, as the US president has the authority to declassify information, but it has been seen by many in the intelligence community as a breach of trust.
Reactions in brief
- "This is dangerous and reckless" - Dick Durbin, Senate's second-highest ranked Democrat
- "Mr President, this isn't about your 'rights', but your responsibilities. You could jeopardise our sources, relationships and security" - Adam Schiff, top Democrat on House Intelligence Committee
- "A troubling signal to America's allies and partners around the world and may impair their willingness to share intelligence with us in the future" - Republican Senator John McCain
- "We have no way to know what was said, but protecting our nation's secrets is paramount" - spokesperson for Republican House Speaker Paul Ryan
- Congress could do with "a little less drama from the White House" - Mitch McConnell, Senate majority leader
- "We generally do not want to have anything to do with this nonsense" - Dmitry Peskov, Kremlin spokesman
- "If true, this is not going to instil confidence in allies already wary of sharing the most sensitive information" - senior Nato diplomat quoted by Reuters
Leading Republicans and Democrats have voiced concerns over what was said, with top Senate Democrat leader Chuck Schumer calling for the transcripts to be released by the White House.
The US Senate Intelligence Committee also asked for copies of any notes taken in the meeting.
Pressed by reporters on Tuesday, National Security Adviser HR McMaster declined to say whether or not Mr Trump had shared classified information with the Russians.
He denied the US president had caused a "lapse in national security".
"What the president discussed with the foreign minister was wholly appropriate to that conversation and is consistent with the routine sharing of information between the president and any leaders with whom he's engaged."
He also said Mr Trump had not been aware of the source of information that was discussed with the Russian officials.
CIA Director Mike Pompeo is due to brief the committee later.
The meeting came a day after Mr Trump fired his FBI chief, James Comey, sparking criticism that he had done so because the FBI was investigating his election campaign's alleged Russian ties.