The parents of a U.S. Muslim soldier killed in Iraq accused the highly controversial Republican presidential candidate Donald Trump of ignorance for his criticism of them after their appearance at the Democratic National Convention.

Ghazala Khan, mother of slain U.S. Army Captain Humayun Khan, took up her own defense on Sunday in an opinion piece in the Washington Post that explained why she stood without speaking on the DNC stage last week as her husband criticized Trump for his comments about Muslims.

“Donald Trump said that maybe I wasn’t allowed to say anything. That is not true,” Mrs. Khan wrote, adding that she decided not to speak at the convention because of her pain over the 2004 death of her son.

“When Donald Trump is talking about Islam, he is ignorant,” she wrote.

Trump stirred bipartisan outrage for his back and forth with the Khans.

The Republican nominee lashed out at Khizr Khan, a U.S. citizen of Pakistani provenance and a Muslim, when Khan told of his war hero son at the convention and took issue with Trump’s call for a temporary ban on the entry of Muslims into the United States.

In an interview aired Sunday on ABC’s “This Week,” Trump cast doubt on why Khan’s wife did not speak.

“She was standing there, she had nothing to say, she probably, maybe she wasn’t allowed to have anything to say, you tell me,” Trump said.

Trump on Sunday tweeted that Khan’s son had died twelve years ago: “Captain Khan, killed 12 years ago, was a hero, but this is about radical Islamic terror and the weakness of our “leaders” to eradicate it!”

Both Democrats and Republicans have criticized Trump’s remarks about the Khans.

“Just when I think, Trump can’t possibly be a bigger jerk, he proves me wrong,” Republican strategist Ana Navarro said on Twitter, adding that Trump’s comments about the Khans were “gross.”

Hillary Clinton, Trump’s Democratic rival in the Nov. 8 election, said at a campaign rally on Saturday that Trump’s comments about the Khans were part of a long history of insulting people.

Trump tweeted Sunday that he had been “viciously attacked” by Khan at the convention. “Am I not allowed to respond?” he asked. The candidate also tried to change the subject to the war itself: “Hillary voted for the Iraq war, not me!”

On CNN on Sunday, Khizr Khan said the couple had received a large outpouring of support after their appearance at the convention. He said people had apparently seen the “blackness” of Trump’s character, adding that Trump’s family needed to “teach him some empathy.”