Syrian insurgents attacked a regime checkpoint with 40 tons of explosives on Monday, killing at least 30 Syrian troops, including two officers.
Videos and images posted by opposition supporters online showed an enormous plume of smoke and earth shooting into the air near a small town as men shouted "Allahu akbar".
Rebels fighting to overthrow President Bashar al-Assad regularly carry out guerrilla attacks against his forces, but the size of the blast, which occurred on Monday, was unusual.
The Syrian Observatory for Human Rights said the blast took place outside the town of Ma'arat al-Nu'man in the northwestern Idlib province.
To carry out the detonation, 60 fighters dug a 300-meter (325-yard) tunnel, over 50 days, under the Sahaba checkpoint in Wadi al-Deif. Four buildings were destroyed, reported EA Worldview.
The operation was carried out by three brigades from the Islamic Front and fighters from the Shields of the Revolution Council, which is linked to the Free Syrian Army.
Tunnel bombs by insurgents have destroyed a series of regime positions over the past year, notably in Aleppo. Sources claims that the Syrian military in Aleppo and some areas of Damascus is digging up streets and drilling wells to counter the tactic.