President Donald Trump is under pressure from US politicians, including his fellow Republicans, to explain why he shared highly sensitive intelligence information with senior Russian officials at a meeting in the Oval Office last week.
US officials said Trump discussed intelligence about Islamic State with Russian Foreign Minister Sergei Lavrov and Russian Ambassador Sergei Kislyak at last Wednesday's meeting.
The officials said the information had been supplied by a US ally in the fight against the militant group. The New York Times identified the ally as Israel.
White House spokesman Sean Spicer said he would not comment on the reports. He also declined to say whether the White House would share transcripts of Trump's meeting with Lavrov with politicians who have asked for them.
The disclosure rocked the administration as it struggled to move past the backlash over Trump's abrupt firing of FBI Director James Comey, whose agency was investigating potential ties between Russia and Trump's 2016 presidential campaign.
The Senate Intelligence Committee has asked the White House for more information about reports that Trump gave intelligence information to the Russians.
While not unprecedented, it is a rare privilege for a foreign minister to be granted bilateral talks in the Oval Office with a US president.
A US president has the authority to disclose even the most highly classified information at will, but US and allied officials said that by giving information to Russia, Trump had endangered cooperation from an ally that has intelligence on Islamic State.
Trump took to Twitter on Tuesday to defend his actions.
"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," Trump tweeted. "Humanitarian reasons, plus I want Russia to greatly step up their fight against ISIS & terrorism."
Trump has frequently said he wants to improve US relations with Moscow, damaged by years of disagreement over Russia's role in Ukraine and its backing for Syrian President Bashar al-Assad.
National security adviser H.R. McMaster said Trump did not know the source of the information he disclosed to the Russians.
Turmoil in the White House in recent weeks has overshadowed Republican legislative priorities such as healthcare and tax reform.
Controversy over Russia has also laid bare sharp divisions between the White House and US intelligence agencies.
