Donald’s Trump’s former campaign manager, Paul Manafort, was told to hand himself over to federal authorities, as was one of his former business associates, it was reported on Monday.

Donald Trump sent an extraordinary fusillade of angry tweets about the investigation into possible ties between his election campaign and Russia, amid reports that the special counsel leading the inquiry could make its first arrests as soon as Monday.

According to the New York Times, Manafort and Rick Gates, who was a junior business partner of Manafort’s, are the first people to face charges in the investigation run by special counsel Robert Mueller into Russian interference in the 2016 presidential election, and the Trump campaign’s possible collusion in that effort.

CNN also reported that Manafort would hand himself over on Monday.

Manafort left his apartment in northern Virginia soon after 8am, shielding his face from television cameras. He entered the FBI field office in Washington at 8.15am, accompanied by his lawyer.

Before becoming Trump’s campaign manager in the summer of 2016, Manafort had extensive business ties to Ukraine, where he represented prominent pro-Moscow figures.

Gates is said to have been involved in setting up subsidiary companies in Cyprus that received money from east European sources. He also worked for the Trump campaign.

Manafort was told to quit his campaign post in August 2016, after just five months in the job, after revelations of his business dealings in Ukraine came to light. Sources told the Guardian at the time that Trump had never really bonded with Manafort.

Gates remained part of the campaign and worked on the Trump inaugural committee. He was reported to have been a frequent visitor to the White House since the Trump administration took office.

It was unclear what charges the two men are facing. The Mueller investigation is a broad inquiry, covering collusion, as well as money laundering and tax evasion.

A spokesman for Manafort did not immediately respond to a request for comment on Monday.

Manafort joined Trump’s insurgent campaign in March 2016, as Republicans faced the possibility of the first contested convention since 1976. The veteran operative helped Trump, who was unprepared for the grinding process of winning delegates, not only win the majority needed but also avoid any unpleasant floor fights in Cleveland.

Although Manafort did not formally assume the reins of the Trump campaign until 20 June, when former campaign manager Corey Lewandowski was fired, Lewandowski said after his ejection: “Paul Manafort has been in operational control of the campaign since 7 April. That’s a fact.”

Manafort also played the decisive role in ensuring that Trump picked the Indiana governor, Mike Pence, to be his running mate.

A longtime Republican operative, Manafort helped guide Gerald Ford to victory against Ronald Reagan in 1976, then worked for Reagan in 1980. He has advised several other Republicans, including former president George HW Bush and Bob Dole, who lost the 1996 election to Bill Clinton. His international career precluded him from taking a position with John McCain’s campaign in 2008.