Nineteen Syrian soldiers have been killed in Turkish drone strikes on Idlib, a UK-based monitor has said.
According to the Syrian Observatory for Human Rights (SOHR), the attacks targeted a military convoy and an army base amid increasing violence.
Turkey also shot down two Syrian fighter jets on Sunday.
Russia, a key backer of the Syrian government, has warned it cannot guarantee the safety of Turkish aircraft in Syrian airspace.
Tensions in Idlib escalated sharply last week when at least 33 Turkish soldiers were killed in an air strike.
The incident sparked fears of a major escalation involving Turkey and Syria’s main military ally, Russia.
The pilots of the two Syrian jets brought down on Sunday parachuted to safety over Idlib province, where Turkish troops and rebels have been clashing with Syrian government forces.
Syria, meanwhile, announced that it had brought down three Turkish drones.
Syrian state news said the country was closing its airspace in the north west of the country and that any aircraft that violated this would “be considered a hostile aircraft which must be downed”.
Turkey, which backs rebels in Idlib, said it had also targeted Syrian air defence systems and dozens of tanks.