Us National security adviser Micheal Flynn has resigned over allegation he discussed US sanctions with Russia before Donald Trump took office.
Mr Flynn is said to have misled officials about his call with Russia’s ambassador before his own appointment.
It is illegal for private citizens to conduct US diplomacy.
US reports said earlier the White House had been warned about the contacts last month and had been told Mr Flynn might be vulnerable to Russian blackmail.
In his letter of resignation (PDF), Mr Flynn said he had “inadvertently briefed the vice-president-elect and others with incomplete information regarding my phone calls with the Russian ambassador” late last year.
The White House has appointed Lt Gen Joseph Keith Kellogg as his interim replacement.
In his first public comments about the controversy, President Trump tweeted on Tuesday: “The real story here is why are there so many illegal leaks coming out of Washington? Will these leaks be happening as I deal on N Korea etc?”
Mr Flynn, a retired army lieutenant-general, initially denied having discussed sanctions with Ambassador Sergei Kislyak, and Vice-President Mike Pence publicly denied the allegations on his behalf.
Credit: BBC NEWS