Prominent anti-Syrian Christian politician Pierre Gemayel was assassinated in a suburb of Beirut on Tuesday, increasing tensions in Lebanon amid a showdown between opponents and allies of Damascus that threatens to topple the government.

Anti-Syrian politicians quickly accused Damascus in the shooting, as they have in previous assassinations of Lebanese opponents of its larger neighbor. Gemayel, the industry minister, was the fifth anti-Syrian figure to be killed in the past two years and the first member of the government of Prime Minister Fuad Saniora to be slain.

The assassination, in an afternoon shooting in Gemayel's mainly Christian constituency of Jdeideh, threatens further instability in Lebanon at a time when Hezbollah and other parties allied with Syria are planning a massing wave of street protests unless Saniora reforms his government to give them more power.

In Washington, the U.S. State Department denounced the assassination as terrorism and an attempt to intimidate Saniora's government. The United States has accused Syria and Iran of plotting to overthrow the government, which is dominated by anti-Syrian politicians.

"We are shocked by this assassination," Undersecretary of State Nicholas Burns told reporters. He said it is very important that those who would use violence to divide Lebanon not be allowed to succeed. "We will give full support to the Saniora government in the days and weeks ahead," Burns said.

Click here to go to FOXNews.com's Mideast Center.

Syria also condemned the assassination. "This despicable crime aims to destroy stability and peace in Lebanon," the state news agency said, affirming Syria's keenness on Lebanon's stability, security and unity.

Damascus' opponents in Lebanon have accused Syria of being behind previous assassinations, particularly that of former Prime Minister Rafik Hariri, who was killed in a massive explosion in downtown Beirut in February 2005. Syria has denied any role.

Gemayel, a 34-year-old member of the Phalange Party, had just left a church and was being driving in his car in Jdeideh when another vehicle slammed to a stop in front of him, causing his car to ram into it, security officials said. Witnesses reported that Gemayel's car was also rammed from behind.

Three gunmen stepped out of the attack vehicles and shot Gemayel at point-blank range with automatic weapons, security officials said.

Footage from the scene showed Gemayel's car, which apparently had been shot at from both sides: the passsenger-side window was completely shattered and the driver's-side window was dotted by nearly a dozen bulletholes, and the front hood was crumpled.

Gemayel's driver, who was wounded but survived, rushed the seriously wounded politician to nearby St. Josephs's hospital. Soon afterward, Voice of Lebanon — the Phalange-run radio station — reported Gemayel was dead.

Hundreds of people gathered at the hospital, and supporters shouted slogans against the pro-Syrian and pro-Iranian Hezbollah and Christian leader Michel Aoun, a rival of the Phalange and an ally of Hezbollah.

Wael Abu Faour, an anti-Syrian lawmaker, told Al-Jazeera television, "We directly accuse the Syrian regime of assassinating Gemayel and hold (Syrian) President Bashar Assad responsible for this assassination ... aimed at sending Lebanon into a civil war."

In an interview with CNN, Saad Hariri, leader of the anti-Syrian parliamentary majority, implicitly blamed Damascus, saying, "We believe the hand of Syria is all over the place." He hailed Gemayel as "a friend, a brother to all of us" and appeared to break down after saying: "we will bring justice to all those who killed him."

Gemayel was the scion of one of Lebanon's most prominent political families and had been expected to carry it into the next generation. His father, current Phalange leader Amin Gemayel, served as Lebanon's president between 1982 and 1988 and his grandfather, the late Pierre Gemayel, led the right-wing Christian Phalanage Party that fielded the largest Christian militia and was allied with Israel during the 1975-90 civil war between Christians and Muslims.

Amin Gemayel's brother, Bashir, was elected president in 1982 but was assassinated days before he was to take office in an explosion.

A stunned-looking Amin Gemayel, speaking to journalists outside the hospital, said his son "died as a martyr for his cause." He urged his supporters not to take vengeance.

The slain Pierre Gemayel was a prominent figure in Lebanon's anti-Syrian bloc, which dominates Saniora's Cabinet and the parliament — and which is now locked in a power struggle with the Muslim Shiite Hezbollah and its allies. He was also a vocal critic of the Shiite Muslim Hezbollah group and Lebanon's pro-Syrian president, Emile Lahoud.

Gemayel was believed to be the youngest legislator in the legislature, elected first in 2000, then re-elected in 2005.

On Sunday, Hezbollah leader Sheik Hassan Nasrallah threatened a wave of street protests aimed at bringing down the govenrment if it ignores the group's demand to form a national unity Cabinet, in which Hezbollah and its allies would have considerable influence and would be able to block major decisions.

Nasrallah accused Saniora's government of falling under the influence of the President Bush's administration and called it "illegitimate" and "unconstitutional."

Gemayel's assassination was the first since Gibran Tueni, prominent anti-Syrian newspaper editor and lawmaker, was killed in a car bomb in December. In June 2005, the journalist and activist Samir Kassir and former Communist Party leader George Hawi were killed in separate car bombings in June last year.

Click here to go to FOXNews.com's Mideast Center.