NATO said it will hold an emergency meeting after Ankara on Sunday accused Syria of downing a Turkish jet in international airspace, raising fears that tensions could soar in the tinderbox region.
While admitting that a Turkish F-4 phantom jet briefly strayed into Syrian territory on Friday, Turkish Foreign Minister Ahmet Davutoglu said it was clearly out of it when it was shot down.
"According to our conclusions, our plane was shot down in international airspace, 13 nautical miles from Syria," he said in a television interview.
"The plane did not show any sign of hostility toward Syria and was shot down about 15 minutes after having momentarily violated Syrian airspace," he said.
Syria did not issue a warning before shooting down the plane, which was on an unarmed training mission to carry out a radar system test.
"The Syrians knew full well that it was a Turkish military plane and the nature of its mission," he said, adding that the plane was flying by itself and was not "on any mission, including information gathering, above Syria."
"Nobody should dare put Turkey's (military) capabilities to the test," Davutoglu warned. "No-one can threaten Turkey's security."
"Turkey will act with restraint but determination," he said. "We will bring this affair before public opinion and international law in the name of Turkey's honour."
NATO said it will hold an emergency meeting on Tuesday following a request from Turkey that invoked Article 4 of the alliance's founding treaty under which members can request a meeting if their security is threatened.
"The North Atlantic Council will meet on Tuesday at Turkey's request," said NATO spokeswoman Oana Lungescu.
And UN Security Council member Britain warned that Syrian President Bashar al-Assad's regime "should not make the mistake of believing that it can act with impunity."
"It will be held to account for its behaviour," Foreign Secretary William Hague said, adding that London was ready to pursue "robust action" at the Security Council.
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"What happened was an accident and not an assault as some like to say, because the plane was shot while it was in Syrian airspace and flew over Syrian territorial waters," Syrian foreign ministry spokesman Jihad Makdissi was quoted as saying by the Al-Watan pro-government daily on Sunday.
On Saturday Turkey acknowledged that the plane may have strayed into Syrian airspace in comments seen as a bid to cool tensions between the former allies.
But it seemed to harden the tone in Sunday's comments, as international calls poured in for restraint and reports said that the wreckage of the plane has been located.
UN chief Ban Ki-moon expressed "his deep concern" about the incident, "particularly about the potential serious implications of this incident for the region" UN spokesman Martin Nesirky said.
In a telephone call with Davutoglu, the UN chief "commended Turkey for the restraint shown in its initial reaction and appreciated Turkey and Syria for conducting a joint search operation."
"The secretary general urged both to continue to address the situation diplomatically" and offered UN support in the "difficult circumstances", the spokesman added.
Syria's staunchest ally Iran has also called for calm.
Tehran "asks both sides to show calm and restraint, and hopes that with tact and tolerance and dialogue this issue will be evaluated and through a peaceful resolution, tranquillity and stability will be preserved in the region," Foreign Minister Ali Akbar Salehi was quoted as saying after speaking to his Turkish counterpart.
Davutoglu has held talks over the incident with counterparts from the United States, the other UN Security Council members as well as Iran and Germany, a diplomatic source said.
Relations between one-time allies Turkey and Damascus have plummeted since the start of the uprising against Syrian President Bashar al-Assad in March 2011.
Prime Minister Recep Tayyip Erdogan has repeatedly criticised Assad's handling of what started out as peaceful protests against the decades-old rule by his family and what has today become a bloody conflict that has left more than 15,000 people killed according to activists.
Earlier this year Turkey withdrew diplomats from its Damascus embassy.
Turkey has taken in more than 30,000 civilians who fled the violence in Syria and earlier this month hosted a key meeting of Syrian opposition activists.
Tensions between the neighbours spiked in April after stray bullets fired on the Syrian side of the border killed two Syrians on Turkish soil.