Turkish fighter jets shot down two Syrian warplanes Turkey and destroyed three Syrian air defense systems, the Turkish Defense Ministry said in a statement on Sunday.

The jets were shot down as they attempted to attack Turkish planes, the ministry said, without giving further details. Turkey bombed Syrian air defense systems after they downed one Turkish armed droned in Idlib, it said.

The fighting in Syria’s Idlib has been escalating since Turkey suffered its biggest single military loss there on Thursday when an airstrike killed at least 33 Turkish soldiers. Turkey made retaliatory strikes against Russian-backed Syrian government forces.

Turkey is fighting to prevent the fall of Idlib, the last rebel bastion in the country, fearing a mass exodus of refugees toward Turkey.