A string of recent bombings in Lebanon, many of them suicide attacks, has raised fears of a homegrown jihadist threat driven by the Syrian civil war across the border.
Since July, a series of ten bomb blasts have hit Lebanon, six of them involving suicide bombers.
The attacks have been claimed by various jihadist groups, some of them linked to organisations fighting across the border in Syria, including Al-Nusra Front in Lebanon, the Abdullah Azzam Brigades and the Islamic State of Iraq and the Levant (ISIL).
The groups say they are targeting Lebanon's Shiite Hezbollah movement for fighting in Syria alongside the regime.
A Lebanese military source, speaking on condition of anonymity, said the growth of jihadist groups was an inevitable result of the Syrian conflict.
"We were expecting it would spread here. If your neighbour's house is on fire, it's no surprise if your house catches on fire too," he told AFP.
"Terrorism has begun, regardless of the reasons and causes," he said.
The source said the different names of the groups meant little on the ground.
"Their ideology is the ideology of Al-Qaeda, and Al-Qaeda's ideology is known for not accepting the other. All of these groups... feed on this ideology," he said.
Lebanon is no stranger to violence, with a 1975-1990 civil war that included a spate of bomb attacks against Western embassies and military targets, some carried out by suicide bombers from the Shiite Hezbollah movement.
Now the tactic has returned to haunt the group, as it has been adopted by Sunni militants bitterly opposed to Hezbollah's decision to fight alongside Syrian President Bashar al-Assad against a Sunni-led rebellion.
"For the Al-Qaeda jihadists, Lebanon provided their logistical needs for Syria. Once they became more powerful and had a supportive environment, they turned the country into a land of jihad," the military source said.
Neighbourhoods considered Hezbollah strongholds have been bombed multiple times, with scores of civilians killed, and in August 2013 a double attack hit the Sunni town of Tripoli.
In an echo of the 2005 assassination of former prime minister Rafiq Hariri, an anti-Syrian political figure was killed in a bombing in downtown Beirut in December.
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"Lebanon has witnessed an alarming increase in jihadi activities in recent months," said Rafael Lefevre, a visiting fellow at the Carnegie Middle East Centre.
"The turning point came last April when Hezbollah recognised (publicly) that it was sending fighters to help the Syrian regime crush the rebels."
He said Lebanon was not yet a major jihadist base, in part because its unique religious diversity "makes the overwhelming majority of its population wary of extremism."
But the country is attractive to jihadists "because the state security apparatus is relatively weak, which enables groups to carry out a range of underground activities."
And he said there was potential recruiting ground in Lebanon because of the "growing number of people disaffected with the Lebanese state, especially in the poverty belts of major urban areas."
The assessment is born out by reports that jihadist groups are particularly active in the impoverished parts of northern Tripoli as well as the Ain al-Helweh Palestinian refugee camp.
On January 25, a previously unknown figure by the name of Abu Sayyaf al-Ansari announced the formation of the Lebanese branch of ISIL, which is fighting in Syria.
He said the announcement was made from Tripoli, which is already the scene of regular clashes between Sunni residents of the Bab al-Tebbaneh district and Alawite residents of neighbouring Jabal Mohsen, who share the same Shiite offshoot faith of Assad.
Local sources say Abu Sayyaf is unknown to security services, religious figures or Salafist groups in Tripoli, but the military source acknowledged a growing jihadist presence there.
"There are reports of Al-Qaeda supporters and recently of the formation of ISIL in the city involving Lebanese, Syrians and some Palestinians from the camps, but so far these groups have no bases or organisational structures," he said.
Ties between Lebanese citizens and groups fighting the Syrian regime already exist, with a unknown number of Sunni Lebanese crossing the border to fight alongside rebel groups.
The military source said Al-Nusra Front, Al-Qaeda's official branch in Syria, had been present in Lebanon since the beginning of the conflict.
And he confirmed that the so-called Al-Nusra Front in Lebanon was linked to its Syrian counterpart.
Lefevre warned that "sporadic jihadi attacks in Lebanon will continue until a settlement between regime and opposition is found in Syria which will facilitate Hezbollah's withdrawal."
But the military source warned that even an end to the conflict in Syria would be unlikely to halt jihadism in Lebanon, calling it "an issue that will take years."