Tony Blair has said a new UN Security Council resolution on Iraq is key to progress in the Gulf state.
Mr Blair talked of a greater role for the UN in Iraq
The prime minister was reporting back to MPs after last week's talks with US President George W Bush in Washington.
Mr Blair pledged the UN would have a "central role" in Iraq and he insisted the coalition would "stay the course" for a 30 June handover of power.
Tory leader Michael Howard said planning for post-conflict Iraq had not been adequate.
Mr Blair also used his appearance in the House of Commons to condemn Israel's assassination of Hamas leader Abdel Aziz al-Rantissi.
And although he welcomed Israel's proposal to withdraw from Gaza and parts of the West Bank, Mr Blair said he remained committed to the 'roadmap' plan as the best way to a Middle East peace settlement.
"The road map remains the best way to peace and disengagement from occupied territory can be an opportunity to return to it," he said.
"Disengagement is not the final step, but an important first step on the road to a final settlement."
Mr Blair's comments after Mr Rantissi was killed, along with two of his bodyguards, in a helicopter missile attack in Gaza City.
Mr Rantissi was recently named among Hamas leaders whose UK assets were frozen by Chancellor Gordon Brown.
On Sunday the prime minister conceded he had not expected the security situation in Iraq would become so unstable.
Speaking to American television following talks with Mr Bush, he said the coalition underestimated resistance.
Mr Blair told MPs that unrest in Iraq was down to a minority with most people wanting peace and stability.
"We are on their side against the small minority of those trying to disrupt this vision," he said.
"We will redouble our efforts to build the necessary capability
of the Iraqis themselves to take increased responsibility for security and law
"We will hold absolutely to the June 30 timetable for handover of
He would also work for a new Security Council resolution to set out the new arrangements, he said.
Mr Blair added: "That is the vision. We will stay the course until it becomes the
reality. I hope the whole international community will come together to support
For the Liberal Democrats, Charles Kennedy expressed concern over the extent Mr Bush was actually listening to representations from the prime minister.
But the Lib Dem leader welcomed the increased role in Iraq for the UN.
The prime minister will not comment on how long he expected British troops to stay in Iraq.
But Brigadier Nick Carter, the British commander in the country, suggested it could be as long as a decade, with Iraqi forces needing help to keep security after the 30 June power handover.
Brigadier Carter said on Monday: "We are in cloud cuckoo land if we think we are going to create
overnight a police force that is accountable to the population.
"Certainly for a number of years to come, Western forces are going to have to
be there. I have to be looking two, three, 10 years out."
A Ministry of Defence spokesman said the 10 years figure had been
"plucked out of the air" and was not based on any plan.
Troops were expected to stay in Iraq in 2005 and possibly longer if they were needed, he added.