Donald Trump allegedly revealed highly classified information to Russian foreign minster Sergei Lavrov and Russian ambassador to the US Sergey Kislyak during an Oval Office meeting last week.
The Washington Post reported on Monday that Trump shared details of intelligence gathered about an Isis threat that had been closely guarded within the United States government and among close US allies.
The report said that while Trump did not describe the specific source used to gather the intelligence, he provided highly classified details, apparently connected to an Isis plot related to the use of laptops on board passenger aircraft.
Top administration officials who attended the meeting swiftly pushed back on the allegations on Monday, saying Trump's meeting with Lavrov consisted only of broad discussions surrounding counter-terrorism.
"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," Rex Tillerson, the secretary of state, said.
"During that exchange, the nature of specific threats were discussed, but they did not discuss sources, methods or military operations."
HR McMaster, Trump's national security adviser, said the president and Russian foreign minister "reviewed common threats from terrorist organisations to include threats to aviation."
"At no time were any intelligence sources or methods discussed and no military operations were disclosed that were not already known publicly," McMaster said in a statement.
Speaking to reporters later at the White House, McMaster added to his statement by saying: "I was in the room. It didn't happen."
However, the original report did not suggest Trump had discussed sources and methods. The allegation is that Trump shared some information about laptops on planes which potentially put a source at risk and was given to the US by an ally who did not give consent for that to be shared with Russia.
After the story broke, the White House did not provide any further specifics on the meeting. US officials also confirmed the Post report to other outlets amid the administration's denials.
Chuck Schumer, the Senate Democratic leader, said the report, if true, was "very disturbing."
"Revealing classified information at this level is extremely dangerous and puts at risk the lives of Americans and those who gather intelligence for our country," Schumer said in a statement. "The President owes the intelligence community, the American people, and Congress a full explanation."
Nancy Pelosi, the House Democratic leader, called for a full briefing to Congress "on the extent of the damage President Trump has done in compromising highly classified code-word intelligence to the Russians."
"Even if President Trump unwittingly blew a highly classified code-word source to the Russians, that would be dangerous enough," she said in a statement. "If the president outed a highly classified code-word source intentionally, that would be even more dangerous."
The Washington Post said that in the aftermath of Trump's meeting, White House officials went into damage-limitation mode with calls to the CIA and National Security Agency (NSA).
The meeting was already under scrutiny because of its timing - a day after Trump's controversial decision to fire FBI director James Comey. Comey had been leading a federal investigation into potential ties between Trump and Moscow, stemming from the US government's conclusion last year that Russia interfered with the 2016 presidential election and sought to boost Trump's candidacy.
Despite an initial insistence by the White House that Trump's abrupt dismissal of Comey was unrelated to the Russia inquiry, the president himself acknowledged in an interview last week that "this Russia thing" was a factor.
Questions were raised about the timing of the Trump's meeting with the Russians, and amplified by the fact that American reporters were barred access to the Oval Office while Russian state media was allowed in. The Kremlin-backed Itar-Tass subsequently shared a number of photographs of Trump entertaining Lavrov and Kislyak.
The information shared with the Russians, according to the Washington Post report, is said to have jeopardised a critical intelligence source and been revealed without the consent of the US partner that provided the information to the US.
Trump's alleged indiscretion drew immediate criticism across party lines.
David Kochel, Jeb Bush's top strategist in the 2016 presidential campaign, tweeted: "John McCain probably revealed less to the KGB in 5+ years of torture at the Hanoi Hilton than Trump did in 5 minutes in the Oval."
Mark Warner, the senior Democrat on the Senate intelligence committee, tweeted: "If true, this is a slap in the face to the intel community. Risking sources and methods is inexcusable, particularly with the Russians."
Trump's apparent sharing of classified information with Russia is particularly noteworthy after he spent much of the presidential campaign criticising Hillary Clinton for her use of a private email server as secretary of state.
The breach of security protocol by the president comes against the backdrop of persistent calls for an independent counsel to oversee an investigation into the way Russia mounted an extensive cyberwarfare operation to influence the election.
The US government has said Russia was behind the hacking of emails of the Democratic National Committee and Clinton campaign chairman John Podesta. Tranches of those emails were released on the website Wikileaks at pivotal moments during the election in an apparent effort to undermine Clinton's campaign.
Responding to the reports of Trump's exchange with the Russians, the Democratic National Comittee said in a statement: "Russia no longer has to spy on us to get information - they just ask President Trump and he spills the beans with highly classified information that jeopardizes our national security and hurts our relationships with allies ...
"If Trump weren't president, his dangerous disclosure to Russia could end with him in handcuffs."
But while Democrats have aggressively zeroed in on potential links between Trump and Russia, the reaction from Republicans has been far more muted. Even as a handful of Republicans expressed concerns over the timing of Trump's move to fire Comey, House speaker Paul Ryan and Senate majority leader Mitch McConnell, the top Republican leaders in Washington, backed the president's decision.
"We have no way to know what was said, but protecting our nation's secrets is paramount," said Doug Andres, a spokesman for speaker Ryan. "The speaker hopes for a full explanation of the facts from the administration."
Senior Republican senator John McCain told CNN that "if it's true, it's obviously disturbing." But he cautioned: "Let's wait and see what this was all about first."
Public opinion has grown for a special prosecutor, with a new NBC/Wall Street Journal poll finding that nearly 80% of Americans believe an independent investigator should be appointed to examine Trump's alleged ties to Russia.