A car bomb exploded in the northern Lebanese port of Tripoli this morning beside a military bus, killing six people and wounding 17.

The bomb attack, the second against a military bus in Tripoli in two months, came two days after a suspected suicide car bomber blew up in Damascus, Syria, killing 17 people in an attack being blamed on Islamist militants.

The bomb was planted in a Renault car and exploded shortly before 8am when a bus carrying Lebanese soldiers passed by in a southern neighbourhood of Tripoli, Lebanon's second largest city.

Lebanese television footage showed dozens of soldiers sealing off the site amid the wreckage of the destroyed Renault. The blast shattered windows, and knocked the targeted bus several yards down the road.

Police said that two of the victims were soldiers while the rest were civilians.

There was no claim of responsibility for the bombing, leaving Lebanese pondering a wide array of potential culprits.

“There are many ongoing operations to destroy the Lebanese army, the Lebanese state, the Lebanese citizen,” said Mosbah Ahdab, a pro-government MP from Tripoli, speaking on LBC television. “It is illogical not to have answers to the question: who is doing these things?”

In August, 18 people died in a similar bomb attack against an army bus in Tripoli, the worst bombing in Lebanon for three years.

Initial suspicions for both bus bombings has fallen on the remnants of Fatah al-Islam, a radical Islamist group which waged a three-month battle against the Lebanese army last year in the Nahr al-Bared Palestinian refugee camp, 10 miles north of Tripoli. Although Fatah al-Islam was eventually crushed, some militants, including its leader, Shaker al-Absi, fled the camp and are believed to be hiding with sympathisers in north Lebanon and other Palestinian refugee camps.

Tripoli has been the scene of sectarian battles since May, pitting Sunni groups which support the Western-backed Lebanese Government against the city's Alawite community which is part of the opposition and has close links to the Alawite-dominated regime in Damascus.

A formal reconciliation was reached this month between the feuding factions in north Lebanon, but sectarian tensions remain high.

Rifaat Eid, the son of the leader of Lebanon's small Alawite community, accused Saudi Arabia of funding Salafi jihadists in north Lebanon, blaming them for the violence.

“The Salafis are like kittens when they are weak, but when they are strong they are like tigers,” he said.

But Salafist leaders in Tripoli insist that the threat of jihadist militancy is exaggerated.

“They say we are fanatics and cite what is happening in Iraq, but this is just propaganda to weaken the Sunnis in Lebanon,” said Sheikh Omar Bakri, the Salafist preacher who fled England in 2005 and today lives in Tripoli.

Last month, Bashar al-Assad, the Syrian President, gave warning that Islamic extremists were destabilising north Lebanon. Two weeks ago, thousands of Syrian troops deployed along the north Lebanon border, triggering fears in Beirut of a possible military incursion.

Those concerns hardened with the car bomb attack in Damascus on Saturday, the deadliest in two decades.

Syrian officials and Syria's state-run press have said that the attack was the work of Islamic militants who entered Syria from a neighbouring country, without revealing which country.

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