Former top adviser to the Trump campaign Rick Gates is expected to plead guilty in special counsel Robert Mueller’s investigation into Russian election interference.

A person close to Gates said he is expected to enter the plea as early as Friday.

The plea could signal that he is planning to co-operate with Mr Mueller.

It comes a day after a federal grand jury in Virginia returned an indictment against Gates and former Trump campaign chair Paul Manafort, accusing them of tax evasion and bank fraud.

It is the second round of charges against the two men. They were charged last October with unregistered lobbying and conspiring to launder millions of dollars they earned while working on behalf of a pro-Russian Ukrainian political party.

Gates is said to have informed family and friends about his decision in a letter.

It would mark the fifth publicly known guilty plea in the special counsel probe into possible collusion between the Trump campaign and the Kremlin during the 2016 presidential election.

The plea also comes quickly on the heels of a stunning indictment last week that laid out a broad operation of election meddling by Russia, which began in 2014, and employed fake social media accounts and on-the-ground campaigning to promote Donald Trump, disparage Hillary Clinton and sow division and discord among the US electorate.

Gates initially pleaded not guilty and had been facing up to 12 and a half years in jail — based on a 12-count indictment handed up in October accusing him and Manafort of acting as unregistered foreign agents and conspiring to launder millions of dollars they earned while working on behalf of a pro-Russian Ukrainian political party.

His guilty plea will almost certainly reduce the prison sentence he could have faced if convicted of all counts at trial.

A sealed charge in the case this week as well as closed-door discussions in recent weeks led to speculation that a plea deal for Gates or some other development might be near.

If Gates agrees to become a co-operating witness as part of a plea deal, he could give Mr Mueller a closer look into Manafort’s years of political consulting work in Ukraine, as well as other events of interest to federal investigators.

Gates had access at the highest levels of the campaign at the same time that Manafort, Donald Trump Jr and Jared Kushner met with a team of Russians in Trump Tower in June 2016. He was also in the top ranks of the campaign when then-senator Jeff Sessions held a pair of undisclosed meetings with Russian ambassador to the US, Sergey Kislyak.