US President Donald Trump's former campaign chief Paul Manafort reported to the FBI Monday amid reports charges have been filed stemming from the US probe into Russian meddling in the 2016 US presidential election.

Manafort and an unidentified man were caught by television cameras walking into the FBI's Washington field office after US media reported he and a longtime associate had been ordered to surrender.

It was not known what charges have been filed in the case, but they would be the first since US special counsel Robert Mueller took over the Russia probe in May.

The New York Times reported that Manafort, who managed Trump's presidential campaign between June and August 2016, and his longtime associate Rick Gates were told to surrender to authorities.

On Sunday, Trump took to Twitter as speculation mounted that charges were about to drop in the Russia probe.

He again complained about his former campaign rival Hillary Clinton's handling of emails while secretary of state, of Democratic Party funding of what he said was a "fake" dossier on Trump's background, and of a US sale during the Obama administration of uranium rights to Russia.

"There is so much GUILT by Democrats/Clinton, and now the facts are pouring out. DO SOMETHING!" Trump tweeted.

Democrats have said the accusations are blatant attempts to divert attention from the Russia probe.

Source: AFP