Suicide bombers attack Air Force intelligence compound on edge of Damascus in the latest sign of Islamist influence

The Free Syrian Army today threatened to “teach a lesson” to Hezbollah leader Hassan Nasrallah by hitting targets in the Lebanese capital as two suicide bombers in vehicles laden with explosives struck a regime intelligence building in Damascus.

In what would constitute a devastating setback to attempts to contain the Syrian civil war, Fahad al Masri, a spokesman for the FSA Joint Command, said rebels would strike Hezbollah in its stronghold in Beirut’s southern suburb of Dahiyeh if the group’s fighters backing President Bashar al-Assad’s forces are not withdrawn immediately.

“If Hezbollah do not stop helping the Assad regime, we will teach Hassan Nasrallah a big lesson inside his area in Beirut,” he told The Independent. “We know how to find him and all the other criminal Hezbollah leaders. I don’t advise Hassan Nasrallah to test our military experience or our knowledge.”

Mr Masri claims that the FSA has captured 13 Hezbollah fighters in the region of Homs over the past two weeks. A long standing ally of the Assad regime, Hezbollah - which is the dominant faction in the Lebanese government and also has an armed wing - has announced several funerals for its fighters in recent weeks, including a senior commander. Hezbollah said the men were killed while performing “jihadist duties” without specifying where. Kamel al-Rifai, a Hezbollah MP, has denied fighters have crossed to Syria.

Compounded by nearly a week of cross-border violence with Turkey, concerns have heightened about how long Syria’s neighbours will be able to remain out of the 19-month old conflict, as daily death tolls regularly push into triple digits.

Speaking in Brussels today, Nato Secretary-General Anders Fogh Rasmussen said the alliance is ready to defend Turkey, in what were regarded as largely symbolic comments.

“Obviously Turkey can rely on NATO solidarity,” he said. “We have all necessary plans in place to protect and defend Turkey if necessary.”

The jihadist group Al Nusra Front claimed responsibility for today’s blast at the Air Force Intelligence building in the Harasta district of Damascus. In a statement the group described how a suicide bomber detonated a car packed with nine tonnes of explosives.

Twenty five minutes later, as authorities rushed to the scene, another bomber in an ambulance carried out a second blast before Al Nusra said it rounded off the attack by “showering” the area with a “barrage of mortar shells”.

Staggered dual bombings, designed to cause maximum loss of life, are a tactic commonly used by al-Qa’ida in Iraq.

“It felt as if a bomb exploded inside every house in the area,“ said one resident. The death toll was unclear, with the area sealed off today, but Syrian Observatory for Human Rights said “dozens” had been killed.

The Air Force Intelligence is one of the most feared branches of the Syrian mukhabarat. It played a key role in the crackdown against the Muslim Brotherhood in the 1980s, and is known for its operations against Islamist groups. Activists raised concerns about the safety of hundreds of prisoners believed to be held in the building.

Al Nusra described it as “one of the most notorious security divisions, and a citadel of repression whose extent is known only to God.”