Donald Trump attempted to head off a mounting Republican rebellion against his nomination of Rex Tillerson as secretary of state by rolling out some of the party’s most respected foreign policy hands to insist the ExxonMobil chief’s ties to Russia did not disqualify him from the job.

Robert Gates and Condoleezza Rice, life-long Russia experts who headed the Pentagon and state department respectively during the George W Bush administration, both endorse the nomination, with Mr Gates calling him a “person of great integrity”.

Mr Trump decided to name Mr Tillerson to the top diplomatic post despite criticisms that his close ties to President Vladimir Putin raised troubling questions at a time US intelligence agencies have determined that Russia waged a cyber campaign to undermine his Democratic rival, Hillary Clinton.

The high-profile endorsements raised the prospect of an internecine confirmation fight over Mr Tillerson, who must be cleared by the Senate before assuming the top diplomatic role.

Republican senators Marco Rubio and Lindsey Graham, former presidential campaign rivals of Mr Trump, joined a phalanx of top Democrats to criticise the Texas oilman because of his ties to Mr Putin. Mr Rubio, a member of the committee that must vet Mr Tillerson’s nomination before it moves to the full Senate, could alone block his approval.

“While Rex Tillerson is a respected businessman, I have serious concerns about his nomination,” said Mr Rubio. “The next secretary of state must be someone who views the world with moral clarity, is free of potential conflicts of interest, has a clear sense of America’s interests, and will be a forceful advocate for America’s foreign policy goals to the president, within the administration, and on the world stage.”