Republican presidential hopeful Donald Trump has attracted outrage by mocking a dead US Muslim soldier's mother.

Ghazala Khan stood silently next to her husband as he attacked Trump in an emotional speech to the Democratic National Convention on Thursday.

 Trump suggested she may not have been allowed to speak.

Republicans and Democrats said the Republican candidate's comments were no way to talk of a hero's mother. s Khan said she was upset by his remarks.

Last week her husband Khizr Khan told Democrats Trump had sacrificed "nothing and no-one" for his country.

At the convention in Philadelphia, he said his son would not even have been in America if it had been up to Trump, who has called for a ban on Muslims entering the US.

Humayun Khan was killed by a car bomb in 2004 in Iraq at the age of 27.

Republican presidential hopeful Donald Trump has attracted outrage by mocking a dead US Muslim soldier's mother.

Ghazala Khan stood silently next to her husband as he attacked Trump in an emotional speech to the Democratic National Convention on Thursday.

 Trump suggested she may not have been allowed to speak.

Republicans and Democrats said the Republican candidate's comments were no way to talk of a hero's mother. s Khan said she was upset by his remarks.

Last week her husband Khizr Khan told Democrats Trump had sacrificed "nothing and no-one" for his country.

At the convention in Philadelphia, he said his son would not even have been in America if it had been up to Trump, who has called for a ban on Muslims entering the US.

Humayun Khan was killed by a car bomb in 2004 in Iraq at the age of 27.

 Trump responded to the criticism in an interview with ABC's This Week.

"If you look at his wife, she was standing there," he said, "She had nothing to say... Maybe she wasn't allowed to have anything to say. You tell me."

But former president Bill Clinton, the husband of Democratic nominee Hillary Clinton, said: "I cannot conceive how he can say that about a Gold Star mother."

Democratic vice-presidential nominee Tim Kaine said Trump's remarks were inappropriate.

"He was kind of trying to turn that into some kind of ridicule," he said, quoted by AP. "It just demonstrates again kind of a temperamental unfitness. If you don't have any more sense of empathy than that, then I'm not sure you can learn it."

Some Republicans also rounded on their candidate.

Ohio Governor John Kasich, a former rival to Trump for the Republican nomination, tweeted: "There's only one way to talk about Gold Star parents: with honour and respect."

In an interview for ABC on Saturday, Ghazala Khan said: "When I was standing there, all of America felt my pain, without a single word. I don't know how he missed that."

"Please Trump, feel that pain and you will be better.

"I was upset when I heard that I didn't say anything because I was in pain."

Khizr Khan said that Trump was "devoid of feeling the pain of a mother who has sacrificed her son".

"Running for president is not an entitlement to disrespect... a Gold Star mother, shame on him," he said.

"He has no decency, he has a dark heart."

Khan said on Friday that she did not speak during her husband's speech because she was still overcome with grief and could not look at her son's photos without crying.

'Tremendous success'

 Trump's campaign issued a statement on Saturday in which he praised Khan’s son Humayun.

"Captain Humayun Khan was a hero to our country and we should honour all who have made the ultimate sacrifice to keep our country safe," he said.

"The real problem here is the radical Islamic terrorists who killed him, and the efforts of these radicals to enter our country to do us further harm."

But Trump rejected Khan's criticism.

"While I feel deeply for the loss of his son, 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, (which is false) and say many other inaccurate things," he said.

In the ABC interview to be broadcast on Sunday, a transcript of which was released by the Trump campaign, Trump was asked what sacrifices he had made.

"I work very, very hard. I've created thousands and thousands of jobs, tens of thousands of jobs, built great structures," he said.

"...I've had tremendous success. I think I've done a lot."

The remarks prompted ridicule on Twitter under the hashtag #TrumpSacrifices, with users listing such hardships as flying commercial class and playing on a municipal golf course.