Syrian insurgents detonated a massive tunnel bomb this week under an intelligence headquarters west of Aleppo in northern Syria, triggering a blast so powerful that European seismologists registered it as a minor tremor.
The explosion Wednesday ushered a ground attack by a coalition of rebel factions on the air force intelligence building that was eventually repelled by Syrian government forces backed by Shi'ite militias, including fighters from the Lebanese militant organization Hezbollah.
The blast could be heard across the city, once Syria’s commercial hub, according to Aleppo civilians contacted via Skype.
Pro-government militiamen and fighters from Lebanon's Hezbollah movement have been pressing an offensive in recent weeks to try to encircle insurgent-held districts of the city, which is split between government forces and the rebels.
The Syrian Observatory for Human Rights, a monitoring group that relies on a network of activists for its information, said at least 20 members of the security forces and 14 insurgents were killed, but added the death toll was rising.
The Syrian army said in a statement that it had “thwarted attempts by terrorist groups to infiltrate the Air Force Intelligence building in Aleppo,” claiming it had “eliminated large numbers of terrorists.” Syrian warplanes also conducted airstrikes to fend off the attackers.
Seismologists take note
The European-Mediterranean Seismological Center registered the blast as a 2.3 magnitude tremor.
The explosion was recorded by the seismologists as taking place at 5:31 p.m. Wednesday just over 8 kilometers west of Aleppo. The tunnel that was packed with explosives ended near the building and destroyed part of it, rebel sources said.
“The goal was to storm the building and to control it, but they failed," said Rami Abdel Rahman, who runs the Syrian Observatory. He described the attack as a blow to the Syrian government, arguing the intelligence building “should have been better protected.”
In a statement on social media, the al-Qaida affiliate in Syria, Jabhat al-Nusra, claimed joint responsibility for the attack, saying its fighters, with help from insurgents with other rebel militias, "stormed the air force intelligence offices and surrounding buildings” on Aleppo’s western outskirts.
The other rebel factions who aided in the assault include Ansar al-Din Front and Ansar al-Khelafa.
Tunneling done before
This isn’t the first time rebels have used the tactic of tunneling near government buildings, command posts or supply routes and setting off explosives, but it is the biggest so far in terms of the force of the blast.
The tactic was first used in the suburbs of Damascus and in the city of Homs. Last year, northern rebels started tunneling under the direction of former carpenter/construction worker Aadil Nasir, who uses the nom-de-guerre “Abu Assad.”
Nasir's handiwork was behind what was previously the largest tunnel explosion in Aleppo, last May, in which the Carlton Citadel hotel, a 150-year-old landmark, was destroyed with 25 tons of explosives. The hotel was being used as a barracks for Syrian soldiers and the 107 meters of tunnel dug for the mining took 33 days.
Other tunnels overseen by Nasir have stretched for more than 800 meters and several targets have been struck in the past few months, including the city’s municipal courthouse; an orphanage used as a barracks by Syrian soldiers; and Aleppo’s police headquarters.
In December a rebel tunnel bomb in Aleppo’s Old City killed at least seven government soldiers.
The tunnel for the bombing of the courthouse took three months to complete and came after several rebel assaults on the building failed to evict Syrian soldiers holding it, according to a Los Angeles Times interview with Nasir last year.
History of tunnel use
The use of tunneling and mining -- a tactic of warfare that goes back to Roman and medieval times -- is testimony to the savagery of the fight in Aleppo.
Successful tunnel bombs in the past have raised the morale of insurgents, who say it is their way of compensating for a lop-sided conflict and of responding to Syrian government forces equipped with more advanced weaponry, such as Scud missiles, warplanes and helicopters.
Tunnel bombs enrage the Syrian military and have inflicted dozens of casualties. But rebel commanders claim government forces have resorted to the tactic too -- although the scale has been less. The tunneling through Aleppo’s rocky earth is challenging and the rebels have been consulting experts in topography for advice on how to excavate and with engineers to ensure the tunnels are stable for diggers to work.
Both the bombing and burrowing is adding to the massive toll the civil war has taken on Aleppo’s centuries-old heritage. More than 120 ancient buildings have been badly damaged or destroyed, according to the United Nations Educational, Scientific and Cultural Organization, UNESCO.