DUBAI, Reuters – Iran declared Wednesday that it would avenge an Israeli airstrike in Syria which resulted in the deaths of four Iranian Revolutionary Guards officers and two civilians.

Syrian state media reported that two of the victims in Monday’s strikes on Damascus were civilians. The British-based Syrian Observatory for Human Rights however identified them as pro Iran Syrian militiamen.

Observatory stated that the Iranian elite Quds Force was responsible for two of the Iranians murdered. The Observatory also stated that six other militiamen were also injured.

Saeed Khatibzadeh from Iran’s Foreign Ministry stated that Israel must be held responsible for attacks like those mentioned.

Sepah News, the Guards website, identified two of the slain officers in its database as Colles Ehsan Karbalaipour (and Morteza Saidnejad), and added that Israel would pay for their crime. It said that their funerals would be held Wednesday.

According to the Observatory, Monday’s strike was Israel’s seventh on Syria in the past year. The target was an ammunition and weapons depot close to Damascus Airport.

Israel is not known for its air strikes on Syria. It has conducted hundreds of them since 2011, when the civil war began.

Iran has been Syrian President Bashar Al-Assad’s most supportive ally throughout the conflict. Backed by Russian air power, Syria’s army and thousands of Iran-backed militias have been fighting insurgents.