The prime minister has vowed to "redouble" British efforts to bring stability to Iraq.

Quizzed by Iain Duncan Smith following the death of six soldiers in the south of the country, Tony Blair said UK troops were assisting in delivering the "prospect of hope for the future".

Their work was of "immense importance to the whole of the region and wider world", he said.

The statement came a day after six service personnel were killed and eight were injured after forces apparently loyal to Saddam Hussein opened fire.

In one incident, which took place near the southern town of Amarah, a British helicopter came under fire after being ambushed by Iraqi rebels.

MoD sources said that they believed the incidents were part of an "orchestrated rebellious attack". They amounted to the second biggest single loss of British lives in Iraq.

The prime minister paid tribute to those who died in the attacks.

"I know the whole house will join with me in sending our deepest sympathy and condolences to those who lost their lives in Iraq," he told MPs.

"They were Royal Military Policemen doing an extraordinary and heroic job in trying to being a normal and decent life to people in Iraq and the whole country and their families can be immensely proud of them even as they mourn them.

"Our thoughts are also with those who were wounded after they were attacked in Iraq yesterday."

The security situation on the ground in Iraq is "serious" despite "real improvements" the prime minister told the Commons.

"It is still obviously serious, because at the present time there are groups, former Ba'athist elements, that are trying to regroup and they post a threat to our troops and particularly the American forces in Baghdad," he told MPs.

"However I think it is also fair to say that as a result of the work that is being done by British troops, Americans and others inside Iraq there are, for example, in Basra now a couple of thousand civilian policemen...back patrolling the streets.

"Although there are tremendous problems, as inevitably there will be, I think it is sometimes important to get a balance of what is happening.

"There are real problems but there are also real improvements.

"It is a job literally of rebuilding a country and it will take time."

The Conservative leader said that Tuesday's attacks should stiffen the coalitions resolve "to bring peace and the rule of law to Iraq".

Duncan Smith said ministers must not walk away and called for a fresh resolve to "enable Iraqis to take control of their own future".

And he praised the "dedication and bravery of our armed forces in Iraq".

Liberal Democrat leader Charles Kennedy also sought reassurances that the international community would commit resources to Iraq, urging Tony Blair to lobby President Putin on the issue during his visit to the UK.

The prime minister said the new United Nations security council resolution on Iraq would bring international support.

"I believe there are around about 19 or 20 countries that have pledged to give added assistance. I've got no doubt at all that we will have a good response to the calls that we are making," Blair added.