Sunni Arab tribesmen have vowed revenge for the killing of a leader who had become a focal point for opposition to al-Qaeda in Iraq.
Abdul Sattar Abu Risha was one of al-Qaeda's top targets
More than 1,500 mourners attended the funeral of Abdul Sattar Abu Risha, who was killed in a bomb attack in the city of Ramadi, Anbar province, on Thursday.
Al-Qaeda in Iraq said later in an internet statement that it had carried out the attack.
Abu Risha had met US President George W Bush in Iraq only 10 days ago.
The alliance he led, Anbar Awakening, has been praised for dramatic improvements in security in Anbar.
Iraq's national security adviser, interior minister and defence minister all attended the funeral in Ramadi, along with the second-in-command of US forces in Iraq, Lt-Gen Raymond Odierno.
The procession was guarded by scores of Iraqi police and US military personnel.
Mourners chanted "We will take our revenge" and "There is no God but Allah and al-Qaeda is the enemy of Allah" as the procession continued to the family cemetery.
Ahmed Abu Risha has been named as the tribal group's new leader after the death of his brother.
He told the Reuters news agency: "All the tribes agreed to fight al-Qaeda until the last child in Anbar."
Sheikh Rashid Majid, a leader of the al-Bufahad tribe in Ramadi, said: "The killing will give us more energy... to continue confronting al-Qaeda members and to dispose of them."
Meanwhile, a suicide lorry bomb killed at least seven people in an attack on two police cars in the northern town of Baiji. Several police officers were among those killed.
Abu Risha was killed in his car, along with two bodyguards, by a roadside bomb planted near his home in Ramadi.
President Bush endorsed Abu Risha on a recent visit
Iraqi National Security Adviser Mowaffaq al-Rubaie said: "It is a national Iraqi disaster. What Abu Risha did for Iraq, no single man has done in the country's history."
The White House also condemned his assassination as "an outrage".
Anbar Awakening, or the Anbar Salvation Council, is an alliance of clans that sided with US forces and the Iraqi government in order to try to reclaim Anbar province from al-Qaeda.
Anbar was once controlled by the insurgents, and was where they declared an "Islamic State of Iraq".
It was one of the deadliest parts of Iraq for US troops.
But the tribal alliance managed to force the insurgents back and reduce violence.
Abu Risha said last week: "I wish we could do in all the provinces of Iraq what we did in Anbar, which is that the people and the government come together."