The chief US administrator in Iraq has said he wants to accelerate the handover of authority to Iraqis.
US deaths in post-war Iraq are greater than during the conflict
Paul Bremer told a news conference in Baghdad his aim was to give Iraqis a "path and a timeline" for the transfer of power from the US-led coalition.
He also promised to speed up the training of Iraqi soldiers and police to respond to ongoing attacks.
Mr Bremer said he believed Saddam Hussein was alive in Iraq, and catching or killing him was a "top priority".
There has been an increase in the number of attacks on US-led troops in Iraq recently but Mr Bremer said he had no clear indication that the ousted Iraqi leader was behind them.
In the latest incident, two American soldiers were killed and two others wounded in an explosion in the northern Iraqi city of Mosul.
A crude bomb or landmine exploded by the side of a road as a US military convoy was passing.
Saturday morning's attack came exactly six months after US President George W Bush declared major hostilities to be over.
In his weekly radio address on Saturday, Mr Bush said the US was determined to "complete our work in Iraq" despite the attacks.
"Leaving Iraq prematurely would only embolden the terrorists and increase the danger to America," he added.
The BBC's Jill McGivering, in the capital Baghdad, says attacks on American forces occupying Iraq are now averaging about 25 a day.
The past week has seen a particular surge, including a series of bombings in Baghdad on Monday which left 36 people dead - the bloodiest day since the war.
Several police stations were targeted, as well as the Baghdad office of the International Committee of the Red Cross.
POST-WAR: KEY EVENTS
1 May: Bush declares 'major combat' over
13 July: Iraqi Governing Council appointed
22 July: Saddam Hussein's sons Uday and Qusay killed
19 August: UN special representative among 20 killed in attack on UN HQ in Baghdad
29 August: Shia Muslim cleric Ayatollah Mohammed Baqr al-Hakim among 80 killed in bombing in Najaf
27 October: Dozens killed in Baghdad bombings, including attack on ICRC office
1 November: 122 US soldiers killed since 1 May (114 killed during war)
General Ricardo Sanchez, the top US military commander in Iraq, acknowledged the shift in guerrilla tactics to include attacks on civilians and international organisations.
But he dismissed the violence as a "strategically and operationally insignificant surge of attacks".
Our correspondent says many people in Iraq believe that fellow Iraqis could provide stability better than foreign troops.
Ambassador Bremer's remarks were intended to demonstrate his willingness to respond to those concerns, she says.
The top administrator said the coalition was going "to turn sovereignty to the Iraqi people as quickly as practicable".
He gave no specific date, but said that by September of next year, more than 200,000
Iraqis would be involved in the defence of their country.
"It is essential that they [Iraqis] take an essential role in their own defence. This is after all their country, it is their future."
Rumours that militants would mark the six-month milestone on Saturday with new attacks affected life in Baghdad, with several schools and businesses closing down and civil servants staying away from work.
Leaflets had circulated, threatening a day of resistance against the US occupation and the US and Australian diplomatic missions issued security warnings to their nationals.
However, the day passed without major incident in the capital and an air of normality returned in the afternoon.