The attacks took place as Russia’s ally Syria said last week it was resuming military operations in a Russian-led campaign in Idlib, blaming Turkey for not abiding by its commitments under a truce deal. Two earlier drone strikes by militants on Russia’s Khmeimim airbase in northwest Syria were reported last week, resulting in two civilians killed on Thursday and four injured on Monday.

Russia’s military has thwarted the third attack on its airbase in Syria in the past week, Russian news agencies have reported.

Anti-aircraft weapons based in Khmeimim have shot down six drones “at a safe distance,” Interfax quoted Russia’s Defense Ministry as saying Sunday evening.

There were no military or civilian casualties, the ministry added.

Militants have regularly attacked the Khmeimim airbase, which has been operating since Russia launched its military operation in Syria in 2015, the RBC news website reported.

Russian jets joined the Syrian army on April 26 in the biggest offensive against parts of rebel-held Idlib province and adjoining northern Hama provinces in the biggest escalation in the war between Syrian President Bashar al-Assad and his enemies since last summer.

The offensive backed by Russia has killed at least 400 civilians in northwestern Syria and uprooted more than 440,000 people since April, the United Nations says.