Trump had suggested the soldier's mother, who stood by her husband as he spoke at the Democratic convention, had not been allowed to to talk
Veterans' groups and Republicans on Monday savaged Donald Trump's war of words with the parents of a slain Muslim American war hero, the latest example of the presidential nominee making statements considered beyond the pale.
The feud has shaken the US presidential campaign and become a flash point 99 days before the November election that pits Republican Trump against Democrat Hillary Clinton.
Criticism has poured in from outraged veterans groups, relatives of soldiers killed in action, and even President Barack Obama.
The episode has dominated US headlines since last Thursday, when Pakistani immigrant Khizr Khan galvanised the Democratic National Convention with a tribute to his dead son in which he rebuked the Republican nominee for having "sacrificed nothing" for the country.
In an interview aired on ABC Sunday, Trump insisted 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.
On Monday, Trump renewed his assault, tweeting: "Mr. Khan, who does not know me, viciously attacked me from the stage of the DNC and is now all over TV doing the same - Nice!"
The families of 23 other slain US soldiers berated Trump for remarks they called "repugnant and personally offensive".