Republican presidential candidates in the US have clashed in a live TV debate over proposals to regulate immigration.
The key contenders are (from L) Romney, Giuliani and McCain
Speaking in New Hampshire, Rudy Giuliani and Mitt Romney criticised a bipartisan proposal backed by another frontrunner, Senator John McCain.
Mr McCain said the bill met "national security challenges", but Mr Giuliani called it "a typical Washington mess".
The 10 candidates also debated the possibility of military strikes against Iranian nuclear facilities.
All candidates agreed that Iran needed to be prevented from developing nuclear weapons and there was criticism of Democratic rivals over their willingness to hold direct talks with Iran on the issue.
California congressman Duncan Hunter was the most explicit, promising that he would be prepared to authorise a tactical nuclear strike if necessary.
However, the most heated exchanges during the debate were sparked by the controversial immigration bill.
"The litmus test you should have for legislation is - is it going to make things better? When you look at these compromises it is quite possible it will make things worse," Mr Giuliani said.
Mr McCain defended the bill, which he co-sponsored by Democratic Senator Edward Kennedy and which is backed by President George W Bush.
He said he had to make compromises in order to draft legislation which both parties would support.
"This isn't the bill that I would have written, but it does satisfy our national security challenges which are severe and intense," he said.
Ex-Massachusetts governor Mitt Romney, said the bill would grant an amnesty to illegal immigrants and was unfair to the thousands seeking to come legally.
If passed by Congress, the bill could give legal status to some of the estimated 12 million illegal immigrants in the US.
President George W Bush and a bipartisan group of senators crafted a compromise version that would also strengthen security along the border with Mexico.
The Iraq war featured early in the two-hour debate, with Senators McCain and Sam Brownback admitting they had not read the detailed report known as the National Intelligence Estimate before authorising the invasion of Iraq.
The revelation drew criticism from another candidate, former Virginia Governor Jim Gilmore.
Thousands of extra US troops are being sent to Baghdad
Mr McCain stood by the decision to invade Iraq, arguing that sanctions designed to prevent Saddam Hussein from acquiring weapons of mass destruction had failed.
Each of the candidates was asked what action they would take if the current US troop surge did not stem the violence in Iraq.
Mr McCain said an early withdrawal of US troops would be disastrous for the entire region.
Mr Romney said the US must work to stabilise the central government in Iraq, in order for the US to bring its troops home as soon as possible.
Mr Brownback said he would end the fighting by splitting Iraq into three states.
The only Republican candidate to call for an immediate withdrawal was Texas Congressman Ron Paul, saying: "It was a mistake to go so it is a mistake to stay."
Not present at the debate but hovering over the proceedings was the fourth frontrunner, the former Tennessee senator and actor, Fred Thompson.
Correspondents say he will not formally declare his candidacy for another few weeks but he looks set to be a serious contender when he does.
New Hampshire is the state holding America's first primary vote next January. Americans will elect a new president in November 2008.