Hillary Clinton's campaign on Thursday accused Republican presidential nominee Donald Trump of "trash-talking" the United States for saying that President Barack Obama founded the Islamic State.
"It goes without saying that this is a false claim from a presidential candidate with an aversion to the truth and an unprecedented lack of knowledge," said Jake Sullivan, a spokesman for Clinton's presidential campaign.
The spokesman said it was "remarkable" that Trump's comments echoed the talking points of Russian President Vladimir Putin and US adversaries "to attack American leaders and American interests, while failing to offer any serious plans to confront terrorism or make this country more secure."
The Republican nominee for president made the accusation against Obama at a rally late Wednesday in Florida, first saying Obama was the "founder" of the group, then said the terrorist organization "honours" him. He then labeled Clinton the "co-founder."
He said the group formed after what he said were mistakes made by the Obama government in the withdrawal from Iraq.
"Normally you want to clean up; he made a bigger mess out of it," Trump said. "He made such a mess."
Clinton, the nominee of Obama's left-leaning Democratic Party, served as his secretary of state from 2009-13.
Trump escalated his attack on Thursday, claiming that if Islamic State were a sports team, Obama and Clinton would be its most valuable players.
A real estate tycoon and reality television star whose blunt talk helped him dominate the conservative party's nomination process, Trump refused to back down from the accusation in a morning radio interview with broadcaster CNBC.
"Is there something wrong with saying that? Are people complaining that I said he was the founder of ISIS?" Trump asked. "Look, all I do is tell the truth. I'm a truth teller."
The comments are the latest in a string of inflammatory remarks by Trump. He set off hand-wringing within the Republican Party by attacking the Muslim-American family of a fallen US soldier and by suggesting that US supporters of the constitutional right to carry a gun might be able to stop Clinton's candidacy.