Russian President Vladimir Putin sought to help Donald Trump win the presidential election, a US intelligence report says.
The unclassified report says the Russian leader "ordered" a campaign aimed at influencing the election.
Moscow has not commented, but Russia has previously denied the claims.
After being briefed on the findings, Mr Trump stopped short of accusing Russia of interfering, saying only that the election outcome was not affected.
The 25-page report says that the Kremlin developed a "clear preference" for Mr Trump.
Russia's goals, the document added, were to "undermine public faith" in the US democratic process and "denigrate" Democratic candidate Hillary Clinton, harming her electability and potential presidency.
"We assess Russian President Vladimir Putin ordered an influence campaign in 2016 aimed at the US presidential election," it said.
The unclassified version contained no detailed evidence of Mr Putin's alleged role, but it said Russia's actions included:
US Attorney General Jeff Sessions has fired FBI official Andrew McCabe, who had been accused of political bias by President Donald Trump.
In January Mr McCabe resigned as deputy director and was placed on leave.
He had been deeply involved in the FBI investigations into Hillary Clinton's use of email and Russia's alleged meddling in the presidential campaign.
The sacking comes two days before his 50th birthday, when he was expected to retire with pension rights.
The move was recommended by an internal investigation, which concluded that Mr McCabe had "made an unauthorised disclosure to the news media".
In a statement issued late on Friday Mr Sessions said: "Based on the report of the Inspector General, the findings of the FBI Office of Professional Responsibility, and the recommendation of the Department's senior career official, I have terminated the employment of Andrew McCabe effective immediately."
Mr McCabe called his dismissal an attack on his credibility, and said it was part of a "larger effort" to discredit the US intelligence community.
He said he believed was being "singled out" because of the events he witnessed and the role he played in the aftermath of the firing of last year of then-FBI director James Comey.
Mr Trump dismissed Mr Comey in July last year over his handling of the inquiry into Mrs Clinton's emails.
But Mr Trump's Democratic critics said he was being punished for the FBI's investigation into alleged links between the Trump presidential campaign and Russia.
Mr Trump has frequently criticised Mr McCabe and in December tweeted: "FBI Deputy Director Andrew McCabe is racing the clock to retire with full benefits. 90 days to go?!!!"