President Joe Biden on Wednesday honoured his uncle and his death in World War II and said Donald Trump was unworthy of serving as commander in chief.

While in Pittsburgh, Biden spoke about his uncle, 2nd Lt Ambrose J Finnegan Jr, aiming to draw a contrast with reports that Mr Trump, while president, had called fallen service members “suckers” and “losers”.

Mr Finnegan, the brother of Mr Biden’s mother, “got shot down in New Guinea,” he said.

The president said Mr Finnegan’s body was never recovered and “there used to be a lot of cannibals” in the area.

President Joe Biden waves returning to the White House after a trip to Pennsylvania. (Susan Walsh/AP)

The US government’s record of missing service members does not attribute Mr Finnegan’s death to hostile action or indicate cannibals were any factor.

“We have a tradition in my family my grandfather started,” Mr Biden said, who was a toddler at the time of his uncle’s death in 1944.

“When you visit a gravesite of a family member — it’s going to sound strange to you — but you say three Hail Marys. And that’s what I was doing at the site.”

Referring to Mr Trump, the presumptive Republican presidential nominee, Mr Biden said, “That man doesn’t deserve to have been the commander in chief for my son, my uncle.”

Mr Biden’s elder son, Beau, died in 2015 of brain cancer, which the president has stated he believes was linked to his son’s yearlong deployment in Iraq, where the military used burn pits to dispose of waste.

Some former officials have claimed the then-president disparaged fallen service members as “suckers” and “losers” when, they said, he did not want to travel in 2018 to a cemetery for American war dead in France.

Mr Trump denied the allegation, saying, “What animal would say such a thing?”