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