US Vice-President Dick Cheney has said he miscalculated how long it would take Iraq to recover from the impact of the Saddam Hussein's rule.
Cheney was sworn in for a second term as vice president
He blamed the brutality of the regime for what he sees as the slowness of Iraqis to "take control of their own affairs" following the US invasion.
Speaking just before his inauguration, Mr Cheney also said Iran was at the top of his list of world trouble spots.
But he made clear he currently favoured diplomacy in dealing with Tehran.
"We don't want a war in the Middle East, if we can avoid it. And certainly in the case of the Iranian situation, I think everybody would be best suited by or best treated and dealt with if we could deal with it diplomatically," Mr Cheney said in the interview, aired on MSNBC.
But if Iran continued to resist demands to rein in its nuclear program - which Tehran insists is solely to produce electricity - the US would seek international sanctions against the country from the UN Security Council, the vice-president warned.
He also suggested that Israel might itself take action against Iran to safeguard its own future - indicating that this would be highly undesirable.
When pressed on mistakes he had made over Iraq, Mr Cheney said he had "miscalculated" the speed of the country's recovery.
This he blamed on the brutality Saddam Hussein had wielded against his own people, emphasising in particular the suppression of the Kurdish and Shia uprisings that followed the 1991 Gulf war.
"The brutality that he used in 1991 to put down the revolt at the time I think just had devastating consequences in terms of the ability of the Iraqi people to recover from his rule," he said.
"It's taken a very long time for them to come back, to take control of their own affairs... I think the hundreds of thousands of people, literally, that were slaughtered during that period of time, including anybody who had the gumption to stand up and challenge him, made the situation tougher than I would have thought."
The Bush administration has been repeatedly criticised by its opponents for not admitting mistakes were made in the handling of the occupation of Iraq.
On Wednesday, President George W Bush's nominee for Secretary of State Condoleezza Rice made a rare acknowledgment that some "bad decisions" were made, while defending the overall invasion.
"We didn't have the right skills, the right capacity, to deal with a reconstruction effort of this kind," she told the US Senate Foreign Relations committee.