Former Australian leader John Howard has said he is embarrassed that the US intelligence on weapons of mass destruction he used to send troops to Iraq in 2003 proved to be unfounded.

But he denied that the conflict, which toppled Saddam Hussein's government, is the main reason for the emergence of Islamic State jihadists in Iraq and neighboring Syria.

Howard, prime minister from 1996 to 2007, said that when he decided to send Australian soldiers to Iraq with US and British forces, it was in the belief that Iraq had WMD.

"I was struck by the force of the language in the US national intelligence assessment late in November 2002," he told the Seven Network in an interview late on Sunday.

"It brought together all the US intelligence, and paragraph after paragraph, they said, 'We judge Iraq has got weapons of mass destruction,' and even talked about potential nuclear capacity.

"Now that wasn't made up. It may have been an erroneous conclusion based on the available information, but it wasn't made up."

No WMD were found in Iraq, undermining the basis for the conflict, which left thousands of Iraqis and foreign soldiers dead.

"I felt embarrassed. I couldn't believe it because I had genuinely believed it. So, I felt embarrassed and I did my best to explain ... that it wasn't a deliberate deception," Howard said.