Turkey was considering its response Saturday after Syria confirmed it had shot down a Turkish fighter jet it said had entered its territory, and both countries searched for the two missing pilots.
In a statement issued after Syria confirmed it had downed the plane, Prime Minister Recep Tayyip Erdogan said Turkey would take all necessary steps once it had established the facts.
Syria's official news agency confirmed that Damascus had downed the jet in a report earlier Saturday.
"An unidentified aerial target violated Syrian airspace, coming from the west at a very low altitude and at high speed over territorial waters" in the eastern Mediterranean, a military spokesman told SANA.
Anti-aircraft batteries had opened fire, hitting the plane as it was one kilometre away from land and it had crashed about 10 kilometres (six miles) off the coast of Latakia province, in Syrian territorial waters, he added.
They had subsequently established that it had been a Turkish fighter and the two countries' navies were now cooperating in an operation to find the two missing pilots, SANA reported.
A little earlier, Erdogan confirmed in a written statement that Syria had shot down a Turkish fighter jet reported missing over the eastern Mediterranean Friday.
The statement was issued after he held an emergency meeting with military and intelligence chiefs and key ministers.
"Turkey will announce its final position and take necessary steps with determination after the incident is entirely clarified," Erdogan added.
A spokesman for the UN Secretary General Ban Ki-moon said he was following the situation closely.
"He hopes this serious incident can be handled with restraint by both sides through diplomatic channels," said Martin Nesirky.
But this latest incident will further test relations between the two neighbours, already strained over Erdogan's outspoken condemnation of Syria's bloody crackdown on anti-government protests.
An earlier Turkish army statement said the jet had lost radio contact with its base over the eastern Mediterranean near Syria's Latakia.
The military plane vanished off radar screens around 0900 GMT after it took off from an airbase in Malatya city in Turkey's southeast.
Malatya governor Ulvi Saran told the Anatolia news agency that the aircraft was a F-4 fighter jet with two pilots on board.
Erdogan's government broke with Damascus regime after his former ally, President Bashar al-Assad, launched a deadly crackdown on popular revolts that erupted mid-March last year.
Syrian activists say the violence has cost more than 15,000 lives.
Turkey has now taken in more than 30,000 civilians who fled the violence in Syria, housing them in camps near the border, according to foreign ministry figures.
Earlier this month, it hosted a key meeting of Syrian opposition activists.
But this latest incident is the most serious yet between the two countries.
"If it is interpreted as an assault on Turkey, the debate over whether to invoke the Article 5 of NATO treaty could resurface," professor Huseyin Bagci told private NTV television.
Bagci was referring to the clause which stipulates that an attack against a member of the North Atlantic Treaty Organisation is considered an attack on all members of the alliance.
Turkey has already considered invoking the NATO article after ricocheting bullets fired on the Syrian side of their common border killed two Syrians on Turkish soil in April.
Also Friday, Ankara denied allegations in a New York Times report that cited US officials and Arab intelligence sources to say that Turkey was among a number of countries shipping weapons to Syrian rebels across the border.
But a report in Saturday's edition of Britain's Guardian newspaper said Turkey had allowed a command centre to be set up in Istanbul to coordinate the supply of weapons to Syrian rebel fighters.
"The centre is believed to be staffed by up to 22 people, most of them Syrian nationals," the report said.
The paper said one of its journalists had witnessed weapons transfers near the border with Syria earlier this month.
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