Several British soldiers also were wounded in the Thursday mortar attack on their base at the airport in the southern city of Basra, the British military said. The two Americans were killed in separate attacks Thursday in the Baghdad area, the U.S. said.

The British deaths bring the number of British soldiers killed in the Iraq war to 162. The much larger American force has lost at least 3,630 service members, according to an Associated Press count.

U.S. and British officials hope that stepped-up military operations around Baghdad will give Iraqi leaders the chance to reach power-sharing agreements to establish a long-term peace in this country.

On Thursday, Sunni legislators returned to parliament after a five-week boycott, raising hopes the assembly can make progress on legislation demanded by Washington before the lawmakers take a month's break in August.

The 44 members of the Iraqi Accordance Front attended Thursday's parliament session after striking a deal with the Shiites and Kurds to reinstate the Sunni speaker, Mahmoud al-Mashhadani, who was ousted by the Shiite-dominated assembly last month for erratic behavior.

Under a face-saving formula, al-Mashhadani is expected to resign after presiding over a few sessions. One official said al-Mashhadani was to step down Wednesday or parliament will force him out. The official spoke on condition of anonymity because of the sensitivity of the information.

The Sunnis returned to the 275-member parliament two days after al-Sadr's 30 lawmakers ended their boycott. Prime Minister Nouri al-Maliki's government accepted the Sadrists' demands for rebuilding a Shiite shrine damaged by bombings.

The two boycotts had paralyzed the legislature, which is under strong criticism from the Americans for failing to approve key legislation and for plans to take a month's vacation in August at a time when U.S. and Iraqi troops are fighting and dying on the battlefield.

In today's violence, four people were killed and three wounded when clashes broke out in the Shiite village of Ajemi near Khalis, 50 miles north of Baghdad, the provincial police said. They said it appeared the village had come under attack by Sunni extremists.

Iraq's national security adviser, meanwhile, raised doubt that the Iraqi security forces would be able to take responsibility for the whole country as had been expected.

"We had hopes and intentions to take over security in all provinces and command of all army divisions before the end of the year," Mouwaffak al-Rubaie told The Associated Press. "But there are difficulties and challenges that appeared along the way, in arming, equipping, recruiting and training our armed forces."

Al-Rubaie would not say how long it would take for Iraqi forces to be able to operate on their own.

"I think it is very difficult to predict a certain time," he said. "This depends on the speed of training and equipping. This depends on the level of threat whether regional or local. But we are not talking about weeks, or not even months. More than months."

Both the Sunnis and the al-Sadr bloc are still refusing to attend Cabinet meetings. And it is also far from certain whether the return of those two factions means approval of major legislative benchmarks can be assured.

For example, several members of al-Sadr's bloc have said they intend to oppose the current draft of the oil bill, which would regulate the country's huge petroleum resources. Companion legislation would distribute oil revenues among all Iraqis, ensuring Sunnis a fair share for their oil-poor regions.

The Kurds also oppose the draft, saying it infringes on their constitutional right to a major role in managing fields and controlling revenues in their northern region. Many Sunnis believe the bill gives too much power to regions.

Sunni leader Adnan al-Dulaimi told the AP the Sunnis had questions about the draft and he did not expect the bill to be debated until September.

Meanwhile, the U.S. ambassador to the United Nations said the U.N. "could play an enormously helpful role" in Iraq.

Zalmay Khalilzad, who also served as U.S. ambassador to Iraq from 2005 to April, wrote in an op-ed piece Friday in The New York Times that the U.N. "possesses certain comparative advantages for undertaking complex internal and regional mediation efforts."

The United Nations has an office and a special representative in Iraq but it cut back severely on its presence here after the Aug. 19, 2003 truck bombing at its headquarters in eastern Baghdad that killed at least 22 people, including the top U.N. official Sergio Vieira de Mello and his deputy, Nadia Younes.

"In the role of mediator, it has inherent legitimacy and the flexibility to talk to all parties, including elements outside the political process," Khalilzad wrote in the Times.