Washington (AFP)

Former US president Donald Trump was indeed hit by an assassin's bullet or a fragment of one, the Federal Bureau of Investigation said on Friday, putting to rest questions over the nature of the Republican candidate's wounding at a campaign rally this month.

"What struck former President Trump in the ear was a bullet, whether whole or fragmented into smaller pieces, fired from the deceased subject's rifle," the FBI said in a statement.

Trump's right ear was covered in blood on July 13 after he was injured during a campaign rally in Pennsylvania.

The FBI deemed the assault -- in which a gunman fired eight bullets from outside the event's security perimeter -- an assassination attempt.

But FBI chief Christopher Wray told US lawmakers on Wednesday that there was some doubt as to "whether or not it's a bullet or shrapnel that, you know, that hit his ear."

Earlier Friday, Trump posted a letter from his former White House doctor saying the wound was almost certainly due to a bullet.

"There is absolutely no evidence that it was anything other than a bullet," wrote Ronny Jackson, now a Republican congressman from Texas, on Truth Social.

Two rally attendees were seriously wounded in the attack, and a 50-year-old Pennsylvania firefighter was shot dead, according to officials. The gunman was killed by a US Secret Service sniper.

At the Republican National Convention where he was anointed the party's nominee for president, Trump said he had "God on my side" as he described the attack.