The Syrian military has admitted it shot down a Turkish fighter plane over the Mediterranean Sea.
But it claims the jet was over Syrian territorial waters.
Earlier, Turkish Prime Minister Recep Tayyip Erdogan held an emergency meeting with his cabinet and the military at his official residence, and formally accused Damascus of downing the plane. His office said search and rescue operations were continuing for the missing pilots.
The Turkish F-4 jet went missing in the middle of the day on Friday after taking off from south-eastern Turkey. Ankara has said it will decide on its response once all the details become clear.
The incident is bound to raise tensions severely between the neighbouring countries.
The violence in Syria has caused thousands to flee to the Turkish border. Many are in refugee camps and there have been skirmishes with the Syrian army.
Turkey has given its backing to the Syrian opposition but has been reluctant to get drawn into the conflict.