Syria shot down a Turkish warplane over the Mediterranean on Friday and Ankara warned it would respond decisively to the incident that threatened a new international dimension to the 16-month revolt against Syrian President Bashar al-Assad.
Syria said the Turkish aircraft was flying low, well inside Syrian territorial waters when it was shot down.
With the second biggest army in NATO, a force hardened by nearly 30 years of fighting Kurdish rebels, Turkey would be a formidable foe for the Syrian army which is already struggling to put down a 16-month-old revolt.
But Prime Minister Tayyip Erdogan's initial comments and subsequent statement on the downing of the F-4 jet were measured in tone. He said Turkish and Syrian forces were working together to search for the two missing crew of the aircraft.
"As a result of information obtained from the evaluation of our concerned institutions and from within the joint search and rescue operations with Syria, it is understood that our plane was brought down by Syria," Erdogan's office said in a statement.
"Turkey will present its final stance after the incident has been fully brought to light and decisively take the necessary steps," the office said after a two-hour emergency meeting between prime minister, the chief of general staff, the defence, interior and foreign ministers, the head of national intelligence and the commander of the air force.
Turkish media had reported earlier that Syria had apologised for the incident, but Erdogan made no mention of an apology.
Violence raged on unabated inside Syria, which appears to be sliding towards a sectarian-tinged civil war pitting majority Sunni Muslims against Assad's minority Alawite sect.
Ankara, which had drawn close to Syria before the uprising against Assad, turned against the Syrian leader when he responded violently to pro-democracy protests inspired by popular upheavals elsewhere in the Arab world. Turkey now gives refuge to the rebel Free Syrian Army on its frontier with Syria.
Erdogan, whose emnity with Assad has assumed a strongly personal nature, gave no hint what action he might contemplate.
A statement by the Syrian military said the Turkish plane was flying low, just one kilometre off the Syrian coast, when it was hit by anti-aircraft fire. The plane fell in Syrian waters seven miles west of the village of Um al-Touyour.
"The navy of the two countries have established contact. Syrian naval vessels are participating along with the Turkish side in the search operation for the missing pilots," it said.
Turkish state television interviewed witnesses on the country's Mediterranean coast, near the Syrian border, who said they saw two low-flying fighter jets pass overhead in the morning in the direction of Syrian waters but only one return.
Ankara has previously floated the possibility of setting up some kind of safe haven or humanitarian corridor inside Syria, which would entail military intervention, but has said it would undertake no such action without U.N. Security Council approval.
Turkey has said however that Assad must go.
Turkey hosts about 32,000 Syrian refugees and allows the rebel Syrian Free Army to operate from its territory. The opposition Syrian National Council meets in istanbul.
Russia and China, Assad's strongest backers abroad, have fiercely opposed any outside interference in the Syrian crisis, saying envoy Kofi Annan's peace plan is the only way forward.
Russian Foreign Minister Sergei Lavrov said after talks with his Syrian counterpart that he had urged Syria to "do a lot more" to implement Annan's U.N.-backed proposals, but that foreign countries must also press rebels to stop the violence.
Lavrov said the Syrian authorities were ready to withdraw troops from cities "simultaneously" with rebels. A Syrian military pullback and a ceasefire were key elements in Annan's six-point peace plan, most of which remains a dead letter.
Annan hit out at some countries he said had taken national initiatives that risked unleashing "destructive competition".
He told a news conference in Geneva that he wanted states with influence on both sides of the conflict to be involved in the peace process, including Iran, Assad's closest ally.
The U.N.-Arab League envoy was speaking a week before a planned Syria crisis meeting that is in doubt because of Western objections to the Islamic Republic's participation.
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