Turkey has described the loss of one of its jets over Syria as "unacceptable" and vowed to take action.
"It is not possible to cover over a thing like this. Whatever is necessary will no doubt be done," Turkish President Abdullah Gul said, as quoted by Reuters.
Turkish and Syrian naval forces are still searching for the F-4 aircraft and its two pilots, who disappeared yesterday over the sea borders of the two countries.
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According to the Associated Press, Gul acknowledged that the jet may have strayed into Syrian airspace as it flew fast and low over the sea, an incident which he suggested was both "routine" and beyond the pilot's control.
Syria's response was "unacceptable," said Faruk Celik, Turkey's Labor and Social Security Minister.
"Even if we assume that there was a violation of Syria's airspace – though the situation is still not clear – the Syrian response cannot be to bring down the plane," the AP cited him as saying.
Syria maintains that it acted "according to laws observed in such cases" by firing anti-aircraft artillery, state news agency SANA reported.
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Turkish Prime Minister Recep Tayyip Erdogan called a meeting between members of the cabinet and military officials this morning to discuss Turkey's response, according to Al Jazeera.
UN Secretary-General Ban Ki-moon is urging both sides to act with restraint and through diplomatic channels, a spokesman told the network.
Many questions remain about the incident, the BBC pointed out, namely where exactly the jet was shot down, what it was doing there, and why Syria shot it down apparently without trying to ascertain its purpose.