US Attorney General Jeff Sessions has withdrawn from any investigations into alleged Russian interference in the 2016 presidential election, won by Donald Trump.
He had faced mounting pressure to stand aside after it emerged that he met last year with Russia's ambassador but did not disclose the contacts in Senate testimony.
Top Republicans had been urging Mr Sessions to remove himself from the FBI probe. Democrats went further and called for his resignation and the appointment of a special prosecutor.
"I have recused myself in the matters that deal with the Trump campaign," Mr Sessions said at a hastily arranged news conference.
It was the latest twist of the controversy over ties between Donald Trump associates and Russia that has dogged the early days of his presidency.
US intelligence agencies concluded last year that Russia hacked and leaked Democratic emails during the election campaign as part of an effort to tilt the vote in Trump's favor. The Kremlin has denied the allegations.
Mr Sessions, the country's top law enforcement official, had testified at his confirmation hearing that he had "no communications with the Russians".
Mr Trump said he stood by Mr Sessions as the political storm erupted. He said he had "total" confidence in the attorney general.
Speaking before the media conference he said he "wasn't aware" Mr Sessions had held two meetings last year with the Russian envoy to the US.
Asked if he thought Mr Sessions should recuse himself from the FBI investigation, he replied: "I don't think so."
Mr Sessions said today he should have told the Senate hearing he had met with the Russian ambassador.
But he said he had been "honest and correct" in his answer to the hearing, drawing a distinction between his role as a senator and his role as a campaign aide.
"I never had meetings with Russian operatives or Russian intermediaries about the Trump campaign."
He had discussed terrorism and the Ukraine with the Russian ambassador to the US, Sergei Kislyak, in a September meeting which he held in his capacity as as a senator, he said.
It has emerged Mr Sessions had also spoken earlier in the summer at a meeting with several other ambassadors. The former Alabama senator had meetings with more than 25 foreign ambassadors in the course of the year.
Mr Kislyak is the same ambassador who led to the downfall of Mr Trump's National Security Adviser, Michael Flynn.
Mr Flynn was fired last month after he misled the White House about his conversations with the Moscow diplomat, allegedly regarding US sanctions.
- BBC / Reuters