Syrian government forces battled to recapture a strategic rebel-held town in Idlib province on Monday and a Turkish official said Ankara would continue to strike President Bashar al-Assad's troops after escalating its military operations at the weekend.
Syrian state television broadcast live footage from inside Saraqeb, which lies on the country's main north-south highway, and said it was under government control. Rebels denied the report, saying they still held the town despite heavy shelling.
Saraqeb has already changed hands twice in less than a month, reflecting its importance both as a gateway to the government-controlled northern city of Aleppo and to the rebel-held Idlib city to the west.
Rebels said Turkish drones had been striking Syrian army positions on the Saraqeb frontline, hitting at least two rocket launchers.
Turkey, which has backed rebels fighting Assad for much of Syria's nine-year conflict, stepped up its intervention in recent days in response to the killing of 34 Turkish soldiers in Idlib.
On Sunday it shot down two Syrian planes in Idlib and struck at least one military airport in Aleppo province, taking the battle deep into territory controlled by forces loyal to Assad.
Defence Minister Hulusi Akar said Turkish forces had also destroyed eight helicopters, scores of tanks and five air defense systems.
"All (Syrian) attacks have been retaliated by the Turkish Armed Forces in the heaviest manner without hesitation and will continue to be retaliated," state news agency Anadolu quoted him as saying.
President Tayyip Erdogan and his Russian counterpart Vladimir Putin, whose support for Assad turned the tide of the war five years ago, are due to meet in Russia on Thursday to seek agreement on Idlib.
Turkey has insisted that it seeks no conflict with Moscow, but its barrage of strikes on the Russian-backed forces around Idlib have raised the risk of a direct confrontation.
"A solution is expected to emerge from the talks but attacks and attempts which the (Syrian) regime carries out in this period will not go unanswered," a senior Turkish security official told Reuters.
Backed by Turkish shelling and drone strikes, rebels say they have now retaken several villages that they lost last week in the Syrian government offensive.
Erdogan demanded in early February that Syrian forces withdraw by the end of the month from a "de-escalation zone" agreed by Turkey, Russia and Iran around Idlib in 2017, or face being driven back by the Turkish military.
"The (Syrian) regime will be forced to leave the de-escalation zone before the Putin-Erdogan meeting," a senior opposition source said.