AMMAN, (Reuters) – Suicide bombers attacked a security compound on the edge of Syrian capital Damascus overnight, in the latest assault by rebels against units loyal to President Bashar al-Assad, insurgents said.

Al-Nusra, a militant Islamist group, claimed responsibility for the attack on the Air Force Intelligence complex in the suburb of Harasta, saying officials working there had played a major role in the government’s crackdown on an 18-month-old revolt.

Residents and opposition activists told Reuters the attack set off huge explosions and was followed by a gun battle. Video footage taken by activists, which could not be independently verified, showed a large explosion.

“The decision was taken to hit Airforce Intelligence because it is one of the most notorious security divisions, and a citadel of repression whose extent is known only to God,” said the statement from Al-Nusra, posted on Facebook.

The Airforce Intelligence unit is commanded by Brigadier General Jamil Hassan, one of Assad’s top lieutenants, and is mostly made up of members of the president’s minority Alawite sect. There was no information on whether Hassan was present during the attack.

Opposition activists said hundreds of Assad’s opponents have been imprisoned without charge and tortured in the Harasta complexes. Human rights groups have also accused rebel forces of torturing prisoners during the revolt.