Republican presidential hopeful Donald Trump drew outrage from Republicans and Democrats by mocking a dead Muslim soldier’s mother who stood silently as her husband attacked him in a speech.
Mr Trump suggested Ghazala Khan may not have been allowed to speak.
Senior politicians said this was no way to talk about the mother of a hero.
In an impassioned speech at last week’s Democratic National Convention, Khizr Khan said Mr Trump had sacrificed “nothing and no-one” for his country.
His son Humayun Khan was killed by a car bomb in 2004 in Iraq at the age of 27
Mr 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 Mr 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 Mr Trump for the Republican nomination, tweeted: “There’s only one way to talk about Gold Star parents: with honour and respect.”
Khizr Khan said in an interview on Saturday that Mr Trump was “devoid of feeling the pain of a mother who has sacrificed her son”, the New York Times reported.
Ghazala Khan said on Friday that she did not speak during her husband’s speech to the Democratic National Convention because she was still overcome with grief and could not look at her son’s photos without crying.
Mr Trump’s campaign issued a statement on Saturday in which he praised Mr 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 are the radical Islamic terrorists who killed him, and the efforts of these radicals to enter our country to do us further harm.”
But Mr Trump rejected Mr Khan’s criticism.
“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, (which is false) and say many other inaccurate things,” he said.
‘Tremendous success’
In the ABC interview to be broadcast on Sunday, a transcript of which was released by the Trump campaign, Mr 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.
Khizr Khan, 65, told the Democratic National Convention in Philadelphia on Thursday that his son had sacrificed his life to save those of his fellow soldiers.
If it had been up to Mr Trump, he said, his son would not have been in America.
Mr Khan asked if Mr Trump had “even read the United States Constitution”, and offered to lend him his copy.