Turkey’s Prime Minister Recep Tayyip Erdogan says its armed forces have shot down a Syrian military jet which had violated its airspace.
The incident reportedly took place in an area where Syrian rebels and government forces have been fighting for control of a border crossing.
Hundreds of thousands have fled Syria for Turkey to escape the three-year uprising against President Assad.
More than 100,000 people have been killed since the Syrian conflict began.
According to UN figures, 6.5 million Syrians have been displaced by the civil war, and 2.5 million are registered as refugees. Lebanon has taken the highest number of refugees, followed by Jordan and Turkey.
Mr Erdogan congratulated his air force on its actions on Sunday.
He told Syria: “Our response will be heavy if you violate our airspace.”
Syria has not commented on the latest incident but earlier issued a statement over alleged Turkish involvement in the Latakia area.
Turkey’s “unjustified military aggression against Syrian sovereignty in the Kasab border region over the past two days proves its implication in the events in Syria”, the foreign ministry in Damascus said.