Jeb Bush has said he would have authorised the US invasion in 2003 of Iraq.

The presumed Republican presidential hopeful said on Sunday he would have authorised the invasion, though he acknowledged mistakes made after Saddam Hussein's downfall.

Bush, the son and brother of two former presidents, pointed out that the Democratic frontrunner Hillary Clinton voted in favour of authorising the use of force in Iraq before the invasion.

"I would have [authorised the invasion], and so would have Hillary Clinton, just to remind everybody," Bush told Fox News television in an interview to be aired late on Monday. "And so would almost everybody that was confronted with the intelligence they got."

Fox News released part of the interview on Sunday.

Bush criticised US policy at the time for failing to focus on security first, saying that led the Iraqis to turn against the military.

But he also denied security was a major point of contention between him and his brother, the then-president George W Bush, who ordered the invasion.

"By the way, guess who thinks that those mistakes took place as well? George W Bush," Jeb Bush said. "Yes, I mean, so just for the news flash to the world, if they're trying to find places where there's big space between me and my brother, this might not be one of those."

The former Florida governor, who has yet to formally announce his candidacy, also discussed immigration.

He is married to Columba Bush, who was born in Mexico; he speaks fluent Spanish and as a young man lived in Venezuela.