Paul Manafort resigned Friday as chairman of Donald Trump's presidential campaign, under fire in connection with a Ukrainian corruption investigation and two days after being sidelined in a team reshuffle.

"This morning, Paul Manafort offered, and I accepted, his resignation from the campaign," the Republican nominee said in a statement, paying tribute to the 67-year-old veteran strategist and lobbyist's skills.

Trump had recruited Manafort, who formerly advised the pro-Kremlin former Ukrainian president Viktor Yanukovych, earlier this year to head off what was then a potentially contested Republican convention.

"I am very appreciative for his great work in helping to get us where we are today, and in particular his work guiding us through the delegate and convention process," Trump said.

"Paul is a true professional and I wish him the greatest success."

On Wednesday, Trump shook up the top tiers of his campaign team for the second time in two months, appointing a right-wing news executive to CEO and promoting a respected pollster to campaign manager.