At least 1000 marines and Iraqi soldiers spearheaded operation Quick Strike, the US military said, in the regions of Haditha, Haqliniyah and Barwanah in western Iraq, where US forces have suffered heavy casualties.
About 40 US soldiers have been killed in western Iraq in the past 10 days, including 14 in a roadside bombing near Haditha, a town 270km northwest of Baghdad.
The military said the operation was an attempt to "disrupt insurgents and foreign terrorists' presence in these regions".
On Friday, a spokesperson said recent intelligence indicated that fighters were operating in these areas, adding: "This morning, Iraqi forces directed an air strike on insurgents hiding in buildings outside of Haqliniyah."
Meanwhile, Iraqi Prime Minister Ibrahim al-Jaafari said the leading Shia cleric Ayat Allah Ali Sistani had expressed willingness for a federal constitution.
"Sistani does not disagree with the principle of federalism if the Iraqi people choose it," al-Jaafari said after meeting the reclusive cleric at his home in the southern town of Najaf.
Ibrahim al-Jaafari (R) met clerics
including Muqtada al-Sadr (L)
The comments could boost hopes of agreement among members of a committee tasked with drafting the constitution by a 15 August deadline.
Aljazeera has learned that al-Jaafari also met with Shia cleric Muqtada al-Sadr in Najaf to discuss the latest on the drafting of the new constitution.
Sources close to al-Sadr said his movement would not directly participate in the political process because of the presence of foreign troops in the country.
Iraq's Kurds, keen to preserve a level of autonomy within their northern territory, are insisting on a federal structure, an issue that has proved divisive for writers of the new post-Saddam constitution.
Many of Iraq's Shia and Sunni Arabs are worried federalism could open the way to a breakup of the country.
Federalism and some other contentious issues were to be discussed at a national conference of Iraqi leaders on Friday in Baghdad.
But the meeting was postponed by two days because of an emergency meeting on Saturday of the Kurdish autonomous parliament.
Mahmud Othman, a Kurdish member of the constitutional committee, said the delay was to permit the Kurdish parliament to discuss the charter.
"There is no way to have a unified Iraq without federalism"
Kurdish regional parliament leader
"We are worried about comments from some on the committee," said Adnan Mufti, head of the Kurdish regional parliament and senior official of Talabani's party.
He said the Kurds were ready to endorse the charter "if all parties understand a constitution should be based on rights for all Iraqis".
He added: "There is no way to have a unified Iraq without federalism."
Other issues to be resolved include official languages, the relation between religion and state, the rights of women and the question of the oil centre of Kirkuk, which Kurds want included in their own autonomous region.
Iraqi leaders have pledged to draft the new basic law by 15 August ahead of a referendum in mid-October, to be followed by national elections in December and the possible formation of a new government by early 2006.
The conference is to report back by 12 August, and any matters still unresolved will be put to parliament for decision by a majority vote.
At least four Iraqis, including two soldiers and a police officer, were killed and 11 wounded in a spate of attacks on Saturday, one of them targeting a US patrol in Baghdad, security sources said.
Clashes between fighters and security forces in the central city of Samarra left two Iraqi soldiers dead and four civilians wounded, Iraqi army Captain Salam Hadi said.
A US patrol was attacked in the
southeast of Baghdad
A civilian was also killed and three more wounded when a shell struck their home in the city, which was recaptured from fighters in a major US-backed offensive late last year, police said.
West of Samarra, the corpses of two Iraqi soldiers were found at the side of a road, the Iraqi army said.
In Baquba, one police officer was killed and another wounded by unknown gunmen while security forces conducted raids in a district where several killings had taken place, police Lieutenant-Colonel Khaled Walid said.
In the capital, three Iraqi civilians were wounded when a bomber blew himself up in a vehicle as a US army patrol was passing, an interior ministry spokesman said.
The attack took place on a road in the southeast of the city but there were no immediate reports of any US casualties.