Washington DC - Former president Barack Obama has told allies that Joe Biden needs to reconsider his reelection bid, the Washington Post reported on Thursday.

Obama believes that Biden's path to victory has diminished and that the 81-year-old should "seriously consider the viability of his candidacy," the newspaper said, citing people briefed on his thinking.

It said there was no immediate comment from Obama, who was in office while Biden was vice president from 2009 to 2017 and who remains hugely influential in the Democratic party.

Obama would be the most heavyweight Democrat so far to join a growing chorus in the party calling for Biden to drop out, following a disastrous debate performance against Donald Trump.

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Biden, who is currently isolating with Covid at his beach house, has rejected concerns about his age and fitness and insisted that he is staying in the race for the White House.

Pressure is mounting, though, with Democratic Senate Majority Leader Chuck Schumer and House Minority Leader Hakeem Jeffries also both reportedly meeting with Biden in recent days to warn that his candidacy threatens his party's prospects in November's election.