Jdeideh, Lebanon ? In a brazen ambush that evoked Lebanon’s civil war, a Cabinet minister and scion of the country’s most influential Christian family was gunned down Tuesday as he drove on a main road in an unmarked car.

Pierre Gemayel, 34, an outspoken critic of Syria and Hezbollah, is the fifth anti-Syrian politician assassinated during the last two years in Lebanon. His killing threatens to unleash sectarian feuds as the country braces for mass protests by Hezbollah and other Syrian allies intent on toppling the U.S.-backed Lebanese government.

The Bush administration denounced the assassination as “an act of terrorism” and said it would continue supporting the government of Prime Minister Fuad Saniora, which was shaken last week when six pro-Syrian ministers resigned.

Often unfazed by political murders, Lebanese were shaken by the audacity of Gemayel’s assassins. “It was like a cowboy movie,” said a Lebanese security official at the scene. “The gunmen got out of a jeep, fired their weapons and sped off. Everyone on the street saw them, but no one had time to react.”

Security officials gave this account of the killing: The industry minister had just left a church in the Jdeideh suburb of Beirut and was driving a silver Kia with a bodyguard sitting next to him. A car in front of them slammed to a stop, causing Gemayel to ram into it.

A Honda jeep then cut the politician off from behind and three gunmen stepped out, surrounded the Kia from three sides and fired automatic weapons outfitted with silencers. The car was dotted with nearly a dozen bullet holes, and its front hood was crumpled. The wounded bodyguard took his boss to the hospital, but Gemayel died on the way.

Mourners stand behind a line of candles under crime-scene tape during a vigil. They mourned Tuesday at the Beirut, Lebanon, site where anti-Syrian Christian politician Pierre Gemayel was assassinated earlier in the day.

“It was a Mafia-style execution,” said Seige Abou Halaka, Gemayel’s cousin, adding that the minister changed cars often and varied his routes. “These were professional assassins, and they knew how to adapt to every situation.”

Anti-Syrian politicians quickly blamed the killing on Syria, as they have done with previous assassinations. But Amin Gemayel, the minister’s father and a former Lebanese president, called for calm and urged his supporters not to blame Damascus without evidence. “We don’t want an outburst of emotions and revenge,” he said outside the hospital where his son’s body was taken. “Pierre was martyred for the cause of a free Lebanon, and we want this cause to triumph.”

The Gemayel clan founded the right-wing Phalange party, which fielded the largest Christian militia during Lebanon’s 1975-90 civil war. Hundreds of Phalange supporters gathered Tuesday night at the hospital, chanting anti-Syrian slogans and waving pictures of Gemayel. In some sections of Beirut, party members burned tires and closed roads.

In a tearful eulogy of Gemayel, Saniora said, “I pledge to you that your blood will not go in vain.”