BAGHDAD - Some 1,500 mourners called for revenge Friday as they buried the leader of the Sunni revolt against al Qaeda, who was assassinated by a bomb after meeting with President Bush earlier this month.

An al Qaeda front in Iraq claimed responsibility for the blast that killed Adbul-Sattar Abu Risha, 37, and three companions. A statement posted on the Internet by the Islamic State of Iraq called Abu Risha "one of the dogs of Bush" and described Thursday's killing as a "heroic operation that took over a month to prepare."

The statement could not be independently verified, but it appeared on Web sites commonly used by the insurgents. Al Qaeda earlier killed four of Abu Risha's brothers and six other relatives for working with the U.S. military.

In Diyala province, meanwhile, a bomb exploded near a U.S. military vehicle on Friday, killing four American soldiers, the U.S. command said. They were the first American deaths reported in Iraq since Monday.

Many al Qaeda fighters were believed to have shifted to Diyala after Abu Risha's tribal fighters helped drive them out of their sanctuaries in Anbar province.

Scores of Iraqi police and U.S. military vehicles lined the route to protect the funeral procession as it followed the black SUV carrying the Iraqi-flag-draped coffin of Abu Risha to the family cemetery just west of Ramadi, Anbar's capital.

"We will take our revenge," the mourners chanted. "We will continue the march of Abu Risha."

The sheik was buried one year to the day after he organized Sunni Arab clans into an alliance to drive al Qaeda in Iraq from sanctuaries in Anbar province where the terror movement had flourished since the U.S.-led invasion in 2003.

Lt. Gen. Ray Odierno, the second-highest ranking U.S. officer in Iraq, and several high-ranking government officials attended the funeral, including Iraq's interior and defense ministers and National Security Adviser Mouwaffak al-Rubaie.

"We condemn the killing of Abu Risha, but this will not deter us from helping the people of Anbar -- we will support them more than before," al-Rubaie declared. "It is a national disaster and a great loss for the Iraqi people -- Abu Risha was the only person to confront al Qaeda in Anbar."

Iraqi officials said the roadside bomb was just outside Abu Risha's walled compound in view of a guard shack and an Iraqi police checkpoint. That raised suspicion that the killing may have been an inside job, the officials said, speaking on condition of anonymity because the information is sensitive.

Sheik Jubeir Rashid, a senior member of Abu Risha's movement, said police were questioning security guards and other staff but no arrests had been announced.

During open-air Friday prayers in the streets of Baghdad's Shiite slum Sadr City, a stronghold of anti-American cleric Muqtada al-Sadr, Imam Muhannad al-Gharawi blamed the assassination on the government's inability to secure Iraq.

"The Iraqi people have lost trust with this government and killings are still going on -- the latest is the assassination of the Anbar Awakening Council leader," he told thousands of worshippers. "Everyone is threatened with death in this country as long as the American Black House is still giving the orders."

Abu Risha's assassination cast a cloud over Bush's claims of progress in Iraq, especially in Anbar, which had been the center of the Sunni insurgency until the dramatic turnaround by the local sheiks. Bush met with Abu Risha during a visit to Anbar on Sept. 3.

In a televised address Thursday, Bush ordered gradual reductions in U.S. forces in Iraq but rejected calls to end the war. More than 130,000 U.S. troops will remain after the withdrawals are completed in July.

Defense Secretary Robert Gates on Friday raised the possibility of cutting U.S. troop levels to 100,000 or so by the end of 2008, if conditions on the ground improve enough.

"It was encouraging to see the president's comments to Americans to reinforce support for us," said Lt. Col. Mike Donnelly, 42, of Honolulu, based at Tikrit with the 25th Infantry Division. "It was encouraging to hear what he had to say because it gives validation to what we're doing."

Capt. Bryan Greening, 25, of El Paso, Texas, said he found no surprises in Bush's speech.

"I think the drawdown is a good idea," said Greening, assigned to Tikrit with the 1st Cavalry Division. "The surge has done whatever it can and now it's time to allow soldiers to go home and get some rest."

In violence Friday, a suicide truck bomb hit a police checkpoint near Beiji, 249 kilometres north of Baghdad, killing four policemen, a Beiji police officer said.

South of Baghdad, gunmen killed three farmers who were taking their turn guarding a village, police said.

Farther south in the city of Hillah, gunmen attacked the home of Col. Hussein Ali Hassoon al Khafaji, an Iraqi army battalion commander, killing a guard and wounding another, police said.

In a helicopter assault west of Baghdad, three suspected insurgents were killed and three American soldiers were injured, the U.S. command said.

Iraqi soldiers led the raid Thursday on a mosque in Karmah, a town in Anbar province, the U.S. military said. The target was a high-ranking al Qaeda in Iraq leader believed responsible for orchestrating murders, sniper attacks and the planting of roadside bombs.

During the operation, people fleeing the mosque fired at American troops, wounding three. U.S. and Iraqi forces retaliated with ground fire and close air support, killing three suspected insurgents, the military said.

The military statement did not say whether the al Qaeda figure was among the dead.

In another raid Thursday, U.S. and Iraqi Special Forces killed a Shiite militiaman believed to be leader of about 25 fighters who had shot mortars and small arms at U.S. forces near Diwaniyah, 128 kilometres south of Baghdad, the U.S. command said.

During the raid the leader, Najah Al-Agra -- also known as Abu Ali -- aimed his pistol as if to fire and the Iraqi and U.S. troops shot and killed him, the military said.