United States President Donald Trump reportedly revealed classified information about Isis to the Russian foreign minister in a White House meeting last week.
The story, first broken by the Washington Post, alleges that Trump passed on information provided by a US partner through a confidential intelligence-sharing arrangement, which had been withheld from allies and restricted within the US government.
The partner had not given the US permission to share this information with Russia.
The Washington Post said a US official familiar with the matter disclosed that Mr Trump:
revealed more information to the Russian ambassador than we have shared with our own allies.
H.R. McMaster, the national security adviser, said in a brief statement that the story was "false":
At no time were any intelligence sources or methods discussed, and no military operations were disclosed that were not already known publicly.
He later said:
The story that came out tonight as reported, is false.
I was in the room. It didn't happen.
The story has attracted ire from the media, who see it as indicative of Trump's irresponsible and boastful nature.
Dave Itzkoff, a culture reporter for the New York Times, made the following joke in 2015.
Itzkoff has since revisited the tweet:
People have noticed it's a bit too close to the bone now.
It's all a bit too real.