BEIRUT (AFP) - Turkish drone strikes killed 26 Syrian soldiers in northwestern Syria on Saturday (Feb 29), the Syrian Observatory for Human Rights war monitor said.

Earlier in the day, Turkey's President Recep Tayyip Erdogan threatened reprisals for the killing of dozens of Turkish troops in Syria on Thursday.

"Twenty-six members of the Syrian army were killed when Turkish drones targeted positions of the regime forces in the Idlib and Aleppo countryside," the Britain-based Observatory said.

The apparent retaliation came after 33 Turkish soldiers were killed in an air strike by Syrian regime forces on Thursday.

A 34th soldier later died from his injuries.

Russia-backed regime forces have since December led a military offensive against the last major rebel stronghold of Idlib in northwestern Syria, where Turkey supports some rebel groups.

The onslaught has caused almost a million people - mostly women and children - to flee their homes and shelters, the United Nations says.

Tensions have spiked in recent weeks between Ankara and Moscow, whose relationship has been tested by violations of a 2018 deal to prevent a regime offensive on Idlib.

Turkey deployed troops to man observation posts in northwestern Syria under that deal.

Syria's civil war has killed more than 380,000 people since it started in 2011 with the brutal repression of anti-government protests.