Tony Blair has defended an overnight bombardment by US forces of insurgent positions in the Iraqi city of Falluja.
Blair says US troops had a right to fire back
"It is perfectly right and proper that they take action against those insurgents," he told MPs.
Lib Dem leader Charles Kennedy pressed the PM to use his influence on the US to not just rely on an overwhelming use of force to deal with violence in Iraq.
Mr Blair said: "If American soldiers are being fired on, American soldiers are going to have to fire back."
The prime minister launched the defence of US forces after a night of the most intensive use of firepower in Falluja.
Commanders of US marines besieging the predominantly Sunni Muslim city said the assault was in response to several breaches of the local ceasefire.
Mr Blair said he "deeply regretted" any civilian deaths in Falluja, insisting "but it is necessary that order is restored and the Americans are
trying to do that".
He said the US had made no specific requests for deployment of additional British troops to Iraq, but that the situation was being kept "under constant review".
"At the present time, we believe we have sufficient troops," Mr Blair told MPs at prime minister's questions in the Commons.
'Well armed' terrorists
Mr Blair was responding to challenges from both Tory leader Michael Howard and Mr Kennedy about whether more troops would be
Mr Blair insisted the coalition had a "clear political and military strategy" to achieve sufficient security in Iraq for the political process to work.
He said US forces had been fired on by the insurgents with which they were engaged in military action.
Veteran Tory MP Sir Peter Tapsell asked the prime minister if he supported "the murder and mutilation of hundreds of women and children in Falluja as an appropriate response to the savage murder" of four Americans.
Mr Blair said he did not agree with Sir Peter's "characterisation" of what had happened in the city, arguing that some 19 Iraqi police officers had also been murdered.
He said a large number of "very well armed" former regime elements and outside terrorists were operating in Falluja.
The Americans were trying to restore order with members of the Iraqi governing council and local civil leaders.
"I deeply regret any civilian death in Falluja, but it's necessary that order is restored," said Mr Blair.
Civilians and coalition troops were being killed by car bombs and suicide bombs, he added.
"The people that have been killing civilians in Iraq are not actually the American soldiers,"
American forces, along with Iraqi police and civil defence forces were due to go on patrol in the city on Thursday.
Mr Blair said the vast bulk of people wanted the insurgents to lay down their arms and "allow the proper process of dialogue to take place".
The prime minister has already faced harsh words from 52 former diplomats about his support of US policy on Iraq.
And 108 MPs have expressed "strong concerns" over the US's endorsement of Israel's plans to withdraw from Gaza.
The diplomats said they were spurred to air their concerns after Mr Blair's appearance in Washington alongside US President George Bush two weeks ago.
The prime minister had stood at Mr Bush's shoulder as he expressed his support for Israel's plan to withdraw from the Gaza Strip while leaving settlers in the West Bank.
The diplomats said they had "watched with deepening concern" as Britain followed the US lead in Iraq and Israel and called for a debate in Parliament.