The brother of the top Shiite cleric killed in a bombing last week, himself a member of the U.S.-selected Iraqi Governing Council, blasted coalition forces for lax security Tuesday and asked them to leave the country.

"This force is primarily responsible for all this blood and the blood that is shed all over Iraq every day," said Abdel-Aziz al-Hakim in the eulogy for his brother, Ayatollah Mohammad Baqir al-Hakim, who was killed along with 125 others in the blast outside the Imam Ali mosque (search) in Najaf Friday.

About 400,000 Shiite mourners finished up a two-day march from Baghdad at the funeral, also held in the holy city of Najaf (search).

"The occupation force is primarily responsible for the pure blood that was spilled in holy Najaf, the blood of al-Hakim and the faithful group that was present near the mosque," Abdel-Aziz al-Hakim said in his eulogy.

"Iraq must not remain occupied and the occupation must leave so that we can build Iraq as God wants us to do," he added.

Without many body parts recovered after the bombing, Al-Hakim's relatives buried a symbolic coffin containing his watch, pen and wedding ring in the 1920 Revolution Square, a cemetery set aside for martyrs in the Shiite uprising against British occupation (search).

Mourners scooped up sand from the cemetery to take home as a souvenir.

Al-Hakim's 15 bodyguards, who died with him in the car bombing, were buried in neighboring plots.

Guards in white robes and dark uniforms brandishing Kalashnikov rifles stood every few yards along the roof of Najaf's golden, domed Imam Ali shrine (search).

Black banners of mourning were draped across the mosque.

Police on loudspeakers implored the crowds jammed shoulder-to-shoulder in the streets to allow the truck carrying the ceremonial coffin to pass. Despite their efforts, the truck was unable to make it to the entrance of the mosque.

Pumps sprayed water on the mourners after some fainted from the heat.

Al-Hakim had returned to his native country on May 10 after more than two decades in exile in neighboring Iran.

The bombing that killed him was the country's bloodiest attack since the fall of deposed leader Saddam Hussein. There are varying accounts of how many people died, ranging from more than 80 to more than 120.

The funeral procession started in Baghdad on Sunday and wove its way through Hilla and the second holiest city of Karbala before nearing Najaf for the funeral ceremony.

The moderate Shiite Muslim cleric's son warned Iraq was entering a new, more dangerous era.

"My believing brothers, the sons of Iraq, our injured Iraq is facing great and dangerous challenges in which one requires strength," the ayatollah's son, Mohammed Hussein Mohammed Saeed Al-Hakim, said as the funeral procession made one of its final stops before Najaf in the town of Hilla.

"I call on you to hold on to this unity and help each other ... [through this] new period," he said.

Ansar al-Islam (search), a terrorist group linked to Usama bin Laden's Al Qaeda network, on Tuesday denied any role in the Najaf bombing, an attack on the Jordanian Embassy on Aug. 7 and the one on the U.N. headquarters 12 days later.

"I consider it very unlikely that members of Ansar al-Islam committed such big and grave acts," Mullah Krekar, the group's spiritual leader, told Al-Jazeera television. He added his group's Islamic convictions prevent them from striking such targets.

The report further muddled the issue of who could have perpetrated the attack.

The U.S.-led Coalition Provisional Authority said Najaf Governor Haider Mehadi asked the FBI to join Iraqi police in the investigation, and that the American investigators would be traveling to Najaf shortly.

FBI agents are leading the investigations into both the Aug. 7 bombing of the Jordanian embassy in Baghdad and attack on the U.N. headquarters 12 days later.

The CIA said Monday it was examining a audiotape recording in which a man claiming to be Saddam denied he was behind the Najaf bombing. Al-Hakim was a longtime opponent of Saddam who returned from exile after the U.S. invasion.

The voice on the tape appeared to be that of Saddam and employed his well-known rhetorical flourishes.

"Many of you may have heard the snakes hissing, the servants of the invaders, occupiers, infidels, and how they have managed to accuse the followers of Saddam Hussein of responsibility for the attack on al-Hakim without any evidence," said the tape, broadcast by the Qatar-based Al-Jazeera satellite television station and the Lebanese Broadcasting Corp.

While denying a role in the Najaf bombing, the voice made no mention of the Jordanian Embassy bombing or the U.N. headquarters attack, which investigators suspect may have also been committed by Saddam followers.

Some Iraqi police officials leading the investigation of the bombing have said they believe Al Qaeda-linked Islamic militants were behind the Najaf attack — not Saddam loyalists.

The Associated Press contributed to this report.