A prominent anti-Syrian journalist and lawmaker was killed by a car bomb Monday, a day after returning from France, where he had been staying periodically for fear of assassination.

A previously unknown group claimed responsibility, saying Gibran Tueni was "spreading poisons and lies despite our repeated warnings to him."

Tueni played a major role in the huge demonstrations that, combined with international pressure, forced Syria to withdraw its troops from Lebanon in April, ending a 29-year presence in the neighboring country. Those demonstrations were triggered by a February car bomb that killed former Prime Minister Rafik Hariri.

Tueni's uncle, Telecommunications Minister Marwan Hamadeh, and leading Lebanese politician Walid Jumblatt blamed Syria for the bombing — a charge Syria denied.

Police said Tueni was one of three people killed when a car bomb exploded as his motorcade drove through Mkalles, an industrial suburb of Beirut. The others killed were his driver and an unidentified passer-by.

Another 30 people were wounded in the bombing, which started a fire that destroyed at least 10 vehicles. In the aftermath, church bells tolled and men wept in the street.

Jumblatt said the bombing was intended to silence a voice seeking those responsible for Hariri's assassination. Tueni, 48, was a respected columnist and the general manager of An-Nahar, the country's leading newspaper. His writings often raised the ire of Syria.

"This is a new terrorism message," Jumblatt said.

A previously unknown group, "The Strugglers for the Unity and Freedom in al-Sham," claimed responsibility. Al-Sham is Arabic for the eastern Mediterranean region that includes Lebanon, Syria, Israel and the Palestinian areas.

"We have broken the pen of Gibran Tueni and gagged his mouth forever, turning An-Nahar into a dark night," it said.

"An-Nahar" is Arabic for day.

"He who contemplates attacking those who have sacrificed everything for the sake of Arabism and Lebanon will face the same fate as ... Tueni," the purported claim said.

The statement's authenticity could not be confirmed independently.

Lebanon has been rocked by bombings since Hariri's killing. The attacks have mainly targeted journalists and politicians known to be opposed to Syrian influence in Lebanon.

Monday's attack came a day after the chief U.N. investigator into Hariri's assassination, Detlev Mehlis, delivered his latest report to Secretary-General Kofi Annan. Two U.N. diplomats said the document was expected to raise new questions about Syria's cooperation with that probe.

Mehlis' earlier report, delivered in October, implicated top Syrian and Lebanese security officials in Hariri's killing. Syria denies any involvement and says it is cooperating with the probe.

Preliminary information said Monday's bomb contained 88 pounds of TNT. The blast tossed several cars, including Tueni's armor-plated vehicle, into a ravine and shattered the windows of nearby shops and buildings.

"God have mercy on Gibran and An-Nahar will remain the beacon for freedom," Jumblatt told LBC television.

Tueni's death triggered an outpouring of grief. Bells of Orthodox churches tolled in the Christian quarter of Ashrafieh, Tueni's constituency. Prime Minister Fuad Saniora called an emergency meeting of top security officials and asked the Cabinet to convene later Monday.

Hariri was seen as a quiet opponent of Syria's dominance of the country. His assassination provoked the mass demonstrations against that helped drive Syria out of the country in April.

Hamadeh threatened to withdraw from the Cabinet with two colleagues if the government did not demand a U.N. investigation into the continuing series of bombings. He said there must be an international tribunal to "investigate the continuing crimes of the Syrian regime."

Syrian Information Minister Mehdi Dakhlallah denied his government was involved, telling LBC television: "Those who are behind this are the enemies of Lebanon." Tueni was elected to parliament for the first time in the elections of May and June. He had only returned to Lebanon on Sunday from Paris, where he has been staying most of the past few months out of fear for his safety.

Tueni's grandfather, Gibran Tueni, founded An-Nahar. His father, Ghassan Tueni, is considered the dean of the Lebanese press, having turned the newspaper into an institution respected by friend and foe across the Arab world.

Syria has waged a campaign to discredit the U.N. inquiry since Mehlis' October report.

In an interview broadcast on Russian television Sunday, Syrian President Bashar Assad reiterated his country's innocence and said any attempt to impose sanctions against Syria would destabilize the region.

In his comments to LBC on Monday, Jumblatt said: "Someone told Russian TV that imposing sanctions on Syria would destabilize the Middle East. It looks as if the destabilization has started. But we will respond by continuing to demand the truth."