A roadside bomb packed with nuts and bolts exploded near a bus Wednesday, killing 18 soldiers and civilians in Lebanon's deadliest bombing in more than three years, raising suspicion an Al Qaeda inspired group is seeking to avenge a 2007 military offensive.

The attack in Tripoli, Lebanon's second largest city, cast a dark shadow as Lebanon is trying to make progress in putting years of crisis behind it. Later Wednesday, President Michel Suleiman arrived in Syria in a landmark visit aimed at patching up ties between the rival nations.

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The bomb, detonated by remote control, went off around 8 a.m. during morning rush hour just as the bus pulled to the curb to pick up passengers on a main street in the northern city. It sent metal shrapnel through the bus and the nearby sidewalk crowded with people headed to work.

The bus — which was coming from Akkar, a region further north where many military personnel live — was left pockmarked with holes, its windows blown out. Soldiers and bystanders carried away the dozens of wounded on downtown Banks Street, which was littered with shattered glass.

"I jumped out of my car and saw bodies in the streets," said Nabil Sebaei, owner of the nearby Rivoli theater who was driving to work when the blast went off. "Wherever I saw a body moving, I helped carry them to a car to drive them to the hospital."

"There is no religion in the world that accepts such acts," Sebaei said, visibly shaken.

Suspicion fell on the Fatah Islam, an Al Qaeda-inspired Sunni militant group that the military drove out of the nearby Palestinian refugee camp, Nahr el-Bared, in a monthslong battle in 2007. The fighting killed hundreds of people and destroyed much of the camp.

Fatah Islam leader Shaker Youssef al-Absi, who is still on the run, warned of vengeance in a January audiotape, saying his fighters would "hunt down the followers of Suleiman." who was army commander during the fighting. Al-Absi and four Syrian militants were charged in March for a double bus bombing last year that killed three people.

The army described Wednesday's blast as a "terrorist attack directly targeting the army."

Security officials told The Associated Press that 10 soldiers and eight civilians were killed, and 46 people wounded. A senior military officer had a lower toll of 15 dead, but the security officials said that was because several of the bodies were torn to pieces, complicating the count. All the officials spoke on condition of anonymity because they were not authorized to speak to the media.

The attack came a day after parliament approved a new national unity government joining supporters of Western-backed Prime Minister Fuad Saniora and their top rivals, the Iranian- and Syrian-backed Hezbollah militant group. Many hope the new government will turn a page on the turmoil that has destabilized Lebanon since 2005, at times bringing the country to the brink of civil war.

Saniora vowed that the attack "will not affect the launching of our government" and said "Lebanon and the Lebanese will not kneel ... or submit to the criminals and the terrorists."

Suleiman's visit to Syria for talks with President Bashar Assad is the first by a Lebanese president in three years, seen as a key step forward in improving ties.

Syria long dominated Lebanon, and its opponents in Lebanon accuse it still seeking to control it even after its troops withdrew in 2005, prompted by the uproar over the assassination of former Prime Minister Rafik Hariri.

Lebanon has seen a series of bomb attacks, starting with the 2005 car bomb that killed Hariri, followed by others that have killed well known anti-Syrian figures — but most of those attacks have been targeted assassinations, not aimed at broader casualties. Anti-Syrian Lebanese accuse Damascus in those slayings, though Syria denies any role.

There have been no serious attacks against politicians or public places since February.

Syria's Foreign Ministry denounced Wednesday's explosion and expressed support for Lebanon "against the hands that try to disrupt its security and stability." Lebanon's pro-Syrian Parliament Speaker Nabih Berri said the timing of the explosion before Suleiman's visit aims to prevent "repairing the Lebanese-Syrian relations."

Tripoli, about 50 miles north of Beirut on the Mediterranean coast, has in recent weeks witnessed sectarian clashes between Sunni fighters and followers of the Alawite sect, an offshoot Shiite sect, that killed and wounded dozens of people.

Former Prime Minister Omar Karami, a prominent Tripoli politician, said it is too early to know the motive in Wednesday's bombing, but said the attack could be linked to the 2007 Nahr el-Bared violence, since it appeared to target the military.

Fatah Islam group claimed responsibility for a bomb blast that killed a soldier in Abdeh, near Tripoli, on May 31. Last Friday, about 2,000 supporters of Islamist groups protested in Tripoli to demand the release of prisoners suspected of plotting or carrying out militant attacks in Lebanon.