WASHINGTON: The father of a Muslim American soldier killed in Iraq posed a question to Donald Trump: Have you read the Constitution?

To rapturous cheers, Pakistan-born Khizr Khan fiercely attacked the billionaire businessman Thursday at the Democratic convention in Philadelphia, saying that if it was up to Trump, his son never would have been American or served in the military.

Khan said that Hillary Clinton, by contrast, "called my son the best of America".

The address was the latest effort by Democrats to highlight their diversity and criticise Trump's most contentious plans. Beyond his proposed wall across Mexico, the billionaire businessman has threatened to ban Muslims from entering the United States if he becomes president.

Capt. Humayun Khan died in 2004 when a car loaded with explosives blew up at his compound. He was 27.

Honouring his son, Khizr Khan pulled a copy of the Constitution out of his suit pocket and offered to lend it to Trump.

“Look for the words 'liberty' and 'equal protection of law', he said standing next to his wife, waving the paperback document vigorously.

"Have you ever been to Arlington cemetery?” he then asked. “Go look at the graves of brave Americans who died defending the United States of America. You will see all faiths, genders and ethnicities. You have sacrificed nothing.“

Khan, who moved to the US in 1980, said he and his wife were "patriotic American Muslims with undivided loyalty to our country."

“Like many immigrants, we came to this country empty handed,” he said, believing that with hard work he could raise his three sons "in a nation where they were free to be themselves and follow their dreams".

Trump, Khan argued, was imperilling that ideal with his smears of Muslims, women, judges and other groups. He urged Muslims, immigrants and all patriots to “to not take this election lightly“.

“Vote for the healer,” Khan said, "not the divider".