Trump has 'black soul', says fallen soldier's father

The father of an American Muslim soldier killed in Iraq described Donald Trump as a "black soul" Sunday after the Republican presidential candidate made insulting remarks about the soldier's mother.

Khizr Khan electrified the Democratic convention last week with a tribute to his fallen son that ended with a steely rebuke that Trump had "sacrificed nothing" for his country.

Trump responded in an interview with ABC's "This Week," insisting he had made "a lot of sacrifices" while suggesting that Khan's wife, who stood silent on the convention stage as her husband spoke, had not been allowed to talk.

But Khan shot back in interviews on US television news shows, while his wife Ghazala explained in a Washington Post op-ed that she had been too grief-stricken to speak.

"Without saying a thing, all the world, all America, felt my pain," Ghazala Khan wrote. "Whoever saw me felt me in their heart."

Her son, US Army captain Humayun Khan, was killed in Iraq in 2004 in a roadside explosion at the gates of a military compound.

Khizr Khan, speaking on CNN, accused Trump of lacking the moral compass and empathy needed to be the country's leader.

"He is a black soul. And this is totally unfit for the leadership of this beautiful country," Khan said.

He is not worthy of our comments. He has no decency. He is void of decency, he has a dark heart. - Khizr Khan

Trump has courted controversy and sparked outrage during his drive for the US presidency with disparaging remarks against immigrants, Muslims and women.

His call to temporarily ban Muslims from entering the United States has drawn criticism even from leaders of his own party.

But despite his high negatives he has attracted a fervent following among working class white males, and he stands near even with Democratic candidate Hillary Clinton in the polls.

Khan said he had invited his wife to speak, but she declined, knowing that she would become too emotional.

He said that running for president does not entitle Trump "to disrespect" the relatives of soldiers killed in combat.

"Shame on him! Shame on his family!" he told ABC News. "He is not worthy of our comments. He has no decency. He is void of decency, he has a dark heart."

In a statement late on Saturday, Trump praised Captain Khan as "a hero to our country," but took issue with Khan's convention night speech, including his claim that the billionaire candidate had never read the US constitution.

"While I feel deeply for the loss of his son, Mr Khan, who has never met me, has no right to stand in front of millions of people and claim I have never read the constitution" and "say many other inaccurate things," Trump said.

Clinton criticised Trump's treatment of the Khans during a campaign stop at a church in Cleveland, Ohio.

"Mr. Khan paid the ultimate sacrifice in his family, didn't he?" she told the African American congregation. "And what has he heard from Donald Trump? Nothing but insults, degrading comments about Muslims, a total misunderstanding of what made our country great - religious freedom, religious liberty.”

"It's enshrined in our constitution, as Mr. Khan knows, because he's actually read it," Clinton added.

Agencies contributed to this report.