In a startling breakthrough for prosecutors investigating potential collusion between Russia and the Donald Trump presidential campaign, former national security adviser Michael Flynn announced on Friday that he was cooperating with prosecutors and ready to testify about Russian contacts.

After months of silence and invisibility, Flynn walked into a federal courthouse in Washington DC on Friday morning and pleaded guilty to one count of lying to the FBI. The plea was part of a larger deal with special counsel Robert Mueller’s team, and strikes at the heart of the Trump White House.

The US president was uncharacteristically mute as the spectacle played out. The White House cancelled a planned photoshoot in the Oval Office with the prime minister of Libya.

Flynn admitted that he lied in interviews with FBI agents shortly after the inauguration about conversations he had held with thenRussian ambassador Sergey Kislyak concerning US sanctions on Russia and other matters.

Flynn further described a chain of communication within Trump’s presidential transition team in which he received direction in December 2016 from a “very senior transition official” – unnamed in court documents – and consulted “senior members” of the team on what to say to Kislyak.

Because Trump was not in power at the time, that plotting could expose those involved to charges of working with foreign governments to undermine US policy. But the extent of Flynn’s potential testimony in the Russia matter was unknown and could carry other legal hazards for the White House.

Flynn acknowledged wrongdoing for the first time in a statement on Friday.

“It has been extraordinarily painful to endure these many months of false accusations of treason,” Flynn said. “But I recognize that the actions I acknowledged in court today were wrong, and, through my faith in God, I am working to set things right.”