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Tens of thousands of mourners marched in a funeral procession Thursday for a prominent anti-Syrian legislator killed by a car bomb in a new blow to the stability of Lebanon.

Lawmaker Walid Eido was killed Wednesday as the government began putting together a U.N.-ordered international tribunal to try suspects in the killing of former Prime Minister Rafik Hariri in Beirut two years ago _ a move strongly opposed by Syria and its allies in Lebanon.

Eido was a prominent supporter of the tribunal and a close friend of Hariri. He is the seventh anti-Syrian figure killed in Lebanon in the past two years, starting with the February 2005 death of Hariri in a suicide car bombing less than a mile from Wednesday's attack. Many Lebanese have accused Syria of being behind the slayings, a claim Damascus denies.

Prime Minister Fuad Saniora called for an emergency meeting of Arab foreign ministers and the international community to assist in the investigation of Eido's assassination near a popular waterfront promenade in Beirut.

The slaying was likely to further inflame Lebanon's bitter power struggle between Saniora's Western-backed government and its Syrian-backed opponents, led by the Hezbollah militant group.

Many fear the violence could push the polarized nation, with a fragile balance of ethnic and religious groups, into a new civil war. Eleven people have been killed in government-opposition clashes that took a sectarian Sunni-Shiite tone.

The bomb ripped through Eido's car as he drove from a seaside sports club, also killing his 35-year-old son, two bodyguards and six passers-by _ 10 people in all.

Businesses, schools and government offices were closed Thursday after the government declared a day of national mourning.

The bodies of Eido, his son and a bodyguard were taken in ambulances draped with Lebanese flags from the American University Hospital in West Beirut to a mosque at the Shohada Cemetery several miles away for a prayer service and internment.

Tens of thousands escorted the procession as it passed through the main thoroughfare of Corniche Mazraa in the Muslim sector, where pictures of the slain politicians were posted on walls and overpasses.

Marching behind the ambulances were Hariri's son, Saad, who leads the anti-Syrian majority bloc in parliament to which Eido belonged; Druse politician Walid Jumblatt; and other prominent anti-Syrian leaders.

Mourners waved Lebanese flags, those of Hariri's Future movement and banners of various Sunni factions. The crowds shouted the Islamic cry "There is no God but Allah" and slogans in support of their leaders.

Some applauded or blew whistles as the coffins drove through the packed street of Tarik Jadideh, a Sunni neighborhood loyal to Hariri that was the scene of fierce Sunni-Shiite street clashes in February.

At the mosque, male relatives sobbed and bent to kiss the side-by-side coffins of Eido and his son. The spiritual leader of Lebanon's Sunni Muslim, Grand Mufti of the Republic Sheik Mohammed Rashid Kabbani led the prayers with Saad Hariri at his side.

Hariri said Lebanon will not kneel before the killers and promised they will be brought to justice.

"We fear only God Almighty. We will stay the course with righteousness, justice and calm. But no one should think that this people will kneel and be frightened," he said. "I tell the criminals, 'You will be punished and you will be dragged to prisons and will face justice,' God willing."

Lebanon's majority coalition blamed Syria for Wednesday's assassination.

Syria controlled Lebanon for 29 years until it was forced out after Hariri's assassination, and its Lebanese opponents believe it is seeking to regain domination by plunging the country into chaos.

It was not clear when the funerals of the others would be held as some of the bodies have not been identified yet. Authorities on Thursday identified a lawyer among the dead after running DNA tests.

Hariri had urged his Sunni supporters to keep calm during the funeral, to avoid any eruption of violence.

At the site of the explosion by Beirut's seafront, a dozen Lebanese security agents searched for evidence near four charred cars. Across the street, about 50 angry young men on motorcycles chanted pro-Hariri slogans.

President Bush _ a major Saniora ally _ condemned the bombing and pledged "the United States will continue to stand up for Lebanon, its people, and its legitimate government as they face these attacks."

Bush noted the victims of the spate of attacks "have always been those who sought an end to Syrian President (Bashar) Assad's interference in Lebanon's internal affairs."

He said efforts by both Syria and Iran "to foment instability in Lebanon must stop now."

Wednesday's blast also came as Lebanon is dealing with a separate conflict that threatens to spiral out of control: a nearly four-week battle with al-Qaida-inspired militants barricaded inside a Palestinian refugee camp near the northern city of Tripoli. More than 140 people have been killed in the Lebanese army's siege of the Nahr el-Bared camp.

The Lebanese military and police had already imposed heavy security measures around Beirut in reaction to a series of bombs that have hit the capital since the Nahr el-Bared fighting began. Those explosions killed two people, yet another layer of instability rattling the country.

Headline: National day of mourning declared in Lebanon after anti-Syrian lawmaker assassinated

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The Associated Press contributed to this report.