BEIRUT — The assassination of a prominent Lebanese politician Friday in a bombing in downtown Beirut shattered the illusion that Syria’s tiny neighbor can avoid the brutal violence on the other side of the border as its deeply divided political system continues to take sides in Syria’s conflict.

Mohammed Chatah, a former finance minister and ambassador to the United States, was killed along with his bodyguard and at least four passers-by when a bomb targeted his convoy as he left a meeting of prominent pro-Syrian-rebel politicians in downtown Beirut.

The explosion was the first of its kind to strike Beirut’s ritzy downtown since the 2005 car bombing assassination of Chatah’s close friend and political ally, former Prime Minister Rafik Hariri, and 21 other people. Friday’s blast destroyed several storefronts, blew out windows in exclusive condominiums and luxury hotels and set nearly a dozen cars ablaze after it exploded just before 10 a.m. local time. The bomb rattled windows throughout the city, which has been on edge since two bombs struck the Hezbollah-controlled southern suburbs earlier this year.

In Lebanese political circles, Chatah was seen as a moderate political figure and an economics-orientated technocrat from the Sunni Muslim-majority northern city of Tripoli. Compared with many other members of his political party, the Future Movement, he was considered a less bombastic voice despite his deep opposition to the Syrian regime of Bashar Assad and Assad’s top Lebanese ally, the Shiite Muslim militant group Hezbollah.

The Future Movement, led by Hariri’s son Saad, a former prime minister himself, has been adamant in its support for the Syrian rebels as well as very vocal about the role that Syria and Hezbollah are alleged to have played in the elder Hariri’s death. Releasing a statement from exile in France, Saad Hariri, who refuses to return to Lebanon out of security concerns, declared that Chatah’s killers were the same men who had killed his father.

“Those who assassinated Mohammed Chatah are the ones who assassinated Rafik Hariri, and want to assassinate Lebanon and weaken the state,” he said in the statement.

Five members of Hezbollah are expected to face an international tribunal in The Hague, Netherlands, early next year but they haven’t been apprehended by authorities despite living more or less openly in southern Beirut’s Hezbollah-dominated suburbs.

Lebanon’s support and funding for that tribunal remain a viciously partisan affair in the country’s politics, with Hezbollah and its backers — generally supporters of the Syria regime as well — adamant that the trial shouldn’t be funded by the Lebanese government. Backers of Hariri — and often supporters of the Syrian rebels — have called for the trial to continue and the suspects to be turned over to international authorities.

On Friday many of these backers of Hariri and Chatah’s party called for the most recent assassination to be turned over to that court, but without a functioning government, which collapsed in part from the disputes over Syria and the special tribunal, it remains highly improbable that the new case will be added to that docket or that anyone will be arrested.

In the United States, Secretary of State John Kerry condemned the attack on behalf of President Barack Obama.

“This is a terrible loss for Lebanon, the Lebanese people and for the United States,” Kerry said in a statement. “I had the privilege of spending many hours with Chatah during my visits to Beirut as a United States senator, and I know he was a voice of reason, responsibility and moderation.”

Kerry said the United States supported both the tribunal and “legitimate, unifying” security forces such as the Lebanese Armed Forces.

Lebanon’s inability to form a government has put next year’s presidential election into grave doubt as the two sides can’t agree on how to conduct an election amid a massive political crisis, let alone agree on the country’s traditional method of forming political consensus for the presidency.

Although these are longstanding political rivalries that often turn violent in this fractious nation, the civil war in Syria remains perhaps the gravest threat to Lebanon’s security, with violent incidents coming more frequently and targeting both sides of the divide.

This summer saw two car bombs target Hezbollah-controlled areas, widely thought to be revenge for the group’s participating in Syria’s war, as well as a double suicide bombing of Hezbollah’s key patron Iran’s embassy in Beirut. Chatah’s home city of Tripoli also saw a double car bombing, of two mosques closely associated with support for the Syrian rebels. More than 100 people total died in these incidents.

Rocket fire and small-scale guerrilla attacks by Syrian rebels have targeted Hezbollah-dominated areas along the border with Syria, sparking fears that conventional-style fighting might spread to Lebanon’s economic and political center in Beirut.

In light of these concerns, caretaker Prime Minister Najib Mikati announced Friday that he would cancel his holiday vacation and return to Beirut, in an effort to stop the violence from further spreading.

By nightfall, small-scale clashes between pro-Hariri and pro-Syrian-regime militias reportedly were breaking out in Chatah’s home city of Tripoli.

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