A former top adviser to President Donald Trump’s election campaign has formally pleaded guilty to federal conspiracy and false statements charges in the special counsel’s Russia investigation.

The plea by Rick Gates is a strong indication that he is planning to co-operate with special counsel Robert Mueller’s investigation as it continues to probe the Trump campaign, Russian election interference and Gates’ longtime business associate Paul Manafort.

The 45-year-old Gates made the plea at the federal courthouse in Washington.

He admitted to charges accusing him of conspiring against the US government related to fraud and unregistered foreign lobbying as well as lying to federal authorities in a recent interview.

With his co-operation, Gates gives mr Mueller a witness willing to provide information on Manafort about his finances and political consulting work in Ukraine, and also someone who had access at the highest levels of the Trump campaign.

Paul Manafort maintains his innocence (Jacquelyn Martin/AP)
Paul Manafort maintains his innocence (Jacquelyn Martin/AP)

Gates’ plea came a day after a federal grand jury in Virginia returned a 32-count indictment against him and Manafort, Mr Trump’s former campaign chairman, accusing them of tax evasion and bank fraud.

The indictment in Virginia was the second round of charges against Gates and against Manafort, who has denied any wrongdoing.

The two men were initially 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’ decision marks the fifth publicly known guilty plea in the special counsel probe into possible collusion between the Trump campaign and the Kremlin during the 2016 campaign.

The plea also comes quickly on the heels of the 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 politicking to promote Mr Trump’s campaign, disparage Hillary Clinton and sow division and discord widely among the US electorate.

The charges to which Gates is pleading guilty do not involve any conduct connected to the Trump campaign.

They largely relate to a conspiracy laid out in his indictments, but they do reveal that Gates spoke with the FBI earlier this month and lied during the interview.

That same day, his lawyers filed a motion to withdraw from representing him for “irreconcilable difference”.

The court papers accuse Gates of lying about a March 19 2013 meeting involving Manafort, a lobbyist and a member of Congress.

Gates said the meeting did not include discussion of Ukraine, when in fact prosecutors say it did.

The charges do not name the lobbyist or the lawmaker but filings with the Justice Department show Manafort and lobbyist Vin Weber of Mercury Public Affairs met with Representative Dana Rohrabacher on that date as part of a lobbying campaign on behalf of Ukrainian interests.

On Friday, Manafort said in a statement that he maintains his innocence.

“I had hoped and expected my business colleague would have had the strength to continue the battle to prove our innocence. For reasons yet to surface he chose to do otherwise,” Manafort said.

“This does not alter my commitment to defend myself against the untrue piled-up charges contained in the indictments against me.”

In court filings over the past few months, Gates gradually began to show the strain the case was placing on him and his family.

As Gates was kept on house arrest, he frequently pleaded with US District Court Judge Amy Berman Jackson for leniency to attend sporting events with his four children.

Even on Friday, ahead of his plea, Gates had asked the judge to let him take his children to Boston for spring break so they could “learn about American history in general, and the Revolutionary War in particular”.

On Thursday night, Gates emailed a brief letter to friends and family, telling them of his decision to plead guilty, Republican lobbyist Jack Burkman said.

“It’s sad,” said Burkman, who had hosted a fundraiser for Gates’ legal defence fund.

Under the terms of the plea, Gates is estimated to face between 57 and 71 months behind bars.

Prosecutors may seek a shortened sentence depending on his co-operation.

AP