Washington: Republican presidential hopeful Donald Trump says the invasion of Iraq was possibly the worst decision made by a US president but acknowledged he may have initially supported the move.

‘Bottom line, there were no weapons of mass destruction,’ Trump said during a town hall meeting hosted by CNN that saw the GOP frontrunner take questions from an audience in South Carolina ahead of the state’s primary on Saturday.

‘I’ll tell you very simply. It may have been the worst decision going into Iraq, it may have been the worst decision anybody has made, any president has made in the history of this country, that’s how bad it is,’ he added of the 2003 US invasion.

Trump has slammed former president George W. Bush — whose brother Jeb is a Trump rival in the 2016 race for the White House — on the matter in recent days.

‘The war in Iraq started the whole destabilisation of the Middle East, it started ISIS, it started Libya, it started Syria,’ Trump piled on at the town hall.

‘That was one of the worst decisions ever made by any government at any time. In all fairness, Bush made the decision.’

But in a 2002 interview with radio personality Howard Stern, uncovered by BuzzFeed News, Trump said he would support an Iraq invasion.

‘Yeah I guess so,’ Trump said at the time. ‘I wish the first time it was done correctly,’ referring to the Gulf War of 1990-1991.

When asked at the CNN event if the report was accurate, Trump recognized: ‘I could have said that.’

‘I wasn’t a politician. It was probably the first time anybody asked me that question,’ Trump said, adding that ‘by the time the war started, I was against the war.’