JERUSALEM -- Former Lebanese prime minister Rafik Hariri, a billionaire who helped his country rebuild after its civil war, was assassinated yesterday in Beirut in a car bomb attack on his motorcade that some Lebanese opposition officials blamed on Syria but that analysts said could also have been carried out by an Islamic group, possibly Al Qaeda.
Hariri was among 10 people killed in the explosion at an exclusive seafront neighborhood around 1 p.m. He served as prime minister for 10 of the past 14 years and resigned four months ago amid a power struggle with Lebanon's pro-Syrian president, Emile Lahoud.
Both Syria and Lebanon denied any role in the assassination. Lahoud yesterday decried the assassination as a ''dark point" in Lebanon's history and Syria's official news agency, SANA, quoted President Bashar Assad as saying he ''condemned this horrible criminal action."
The huge blast -- police said 650 pounds of TNT were packed into the car bomb -- caused at least 20 cars, many of them armored, to burst into flames and tore the facades off of several buildings. At least 100 people were wounded.
In a videotape aired on Al-Jazeera television, a previously unknown group calling itself Support and Jihad in Syria and Lebanon claimed responsibility for the attack and accused Hariri, who also had Saudi citizenship and was close to the Saudi royal family, of supporting the Western-leaning regime in Saudi Arabia.
The bombing marked the first time since Lebanon emerged from a 15-year civil war in 1990 that such a high-level politician was killed and raised the specter of new sectarian violence in a country plagued by friction among religious and ethnic groups. The Lebanese Army went on alert and set up checkpoints across the country.
The bombing also was expected to fuel tensions between the United States and Syria, which keeps 15,000 troops deployed in neighboring Lebanon and treats it as a protectorate.
White House Press Secretary Scott McClellan condemned the attack as ''a despicable act." While refusing to assign blame, McClellan said it was time to ''free Lebanon from foreign occupation."
''It's premature to know who was responsible for this attack, but we continue to be concerned about the foreign occupation in Lebanon," McClellan said. ''We've expressed those concerns. Syria has maintained a military presence there for some time now, and that is a concern of ours."
The Associated Press yesterday quoted an unidentified US official as saying that any list of suspects ''would have to include the Syrians and their surrogates in Lebanon." And NBC News cited an unnamed senior State Department official as saying that Margaret Scobey, the US ambassador to Syria, told Syrian officials in Damascus that they needed to stop interfering in Lebanon's internal politics and abide by the UN resolution calling for its withdrawal.
In Israel, Foreign Minister Silvan Shalom said the assassination proves some groups and countries were trying to destabilize the region and block the spread of democracy.
Hariri, who had strong ties to Western governments, donated $10 million to Boston University in 1990 and sat on BU's board of trustees for more than a decade. The BU management school building is named for him.
The 60-year-old Hariri helped engineer Lebanon's political and economic recovery from a bloody civil war during which Beirut was frequently the scene of car bombings and street battles.
He did so in part by accepting the domination of neighboring Syria over his country. Syria's role in Lebanon was strengthened at a summit sponsored by Hariri in Taif, Saudi Arabia, that ended Lebanon's civil war.
But Hariri, a Sunni Muslim, defied Damascus several times in recent months and was said to play a key role in the passing of a UN Security Council resolution last year that called for Syria to pull its troops out of Lebanon.
Two Lebanese opposition figures, Druze chief Walid Jumblatt and Christian ex-President Amin Gemayel, said Syrian and Lebanese authorities bore responsibility for Hariri's death and called on the government to resign. They did not directly accuse Syria or the government of involvement.
A few hundred Lebanese protested yesterday outside the Lebanon branch of the Syrian ruling Ba'ath party, throwing stones and burning pictures of Assad.
''It's clear Syria would have an interest in seeing Hariri eliminated," said Eyal Zisser, a specialist on Syria at Israel's Tel Aviv University. ''He had become a threat to Syria's occupation of Lebanon and he was more dangerous to Damascus than any other leader in Lebanon."
But Zisser said Syria was also trying hard lately not to antagonize Washington, making it less likely that leaders in Damascus would order such an operation. ''They are under heavy American pressure and this is the last thing they need," he said.
Syria is on the US State Department's list of countries that support terrorism, maintains close relations with Iran, and had ties with former Iraqi leader Saddam Hussein. America's invasion of Iraq sparked concern in Damascus that it would also be targeted for military action by the Bush administration.
Moshe Ma'oz, another Israeli specialist on Syria, said relations between Washington and Damascus were at a low point.
''Syria finds itself surrounded by pro-American regimes -- in Turkey, Jordan, Israel, and now Iraq," said Ma'oz, who usually teaches at Jerusalem's Hebrew University but is on sabbatical at the United States Institute of Peace in Washington. ''It is scared stiff of an American attack."
''So what you see now is Syria trying very hard to project an image that it is cooperating with the US, not going around killing political leaders."
Ma'oz said the attack seemed sophisticated enough to rule out small militant groups but he said the Islamic Hezbollah group in Lebanon, which might view Hariri as a political threat, and Al Qaeda, which sees him as too Western, would also be suspects.
President Jacques Chirac of France, a friend of Hariri, demanded an international investigation, saying Hariri represented ''the indefatigable will of independence, freedom, and democracy" for Lebanon.
A man identified by Lebanese authorities as a Palestinian, Ahmed Aboul Adef, read the claim of responsibility in a video aired on Al-Jazeera. He said the attack was a suicide operation and would be followed by more attacks ''against infidels, renegades, and tyrants."
Hours later, Lebanese security forces stormed Adef's Beirut home but he was not there.
Hospital sources said the badly burned Hariri was dead on arrival. Several of his bodyguards were also killed in the blast. Former Economic Minister Bassel Fleihan, who belongs to Hariri's political bloc, was among the wounded and was said to be in critical condition.
Lebanon's top leadership body declared three days of national mourning for Hariri.
Material from the Associated Press and Reuters was used in this report.