Syria confirmed it had shot down a Turkish reconnaissance plane because the plane entered its airspace, insisting it was "not an attack" as both sides desperately tried to de-escalate the episode before it exploded into a regional conflagration.
Turkey threatened to retaliate but did not say what action it would take as it searched for the aircraft's two missing pilots.
The downed plane heightened tensions between two countries that had been allies before Syria's 15-month violent uprising, and signalled that the violence gripping Syria is increasingly bleeding outside its borders.
Germany and Iraq were among the countries urging restraint in the region.
Syria and neighbouring Turkey had cultivated close ties before the Syrian revolt began in March 2011, but since then Turkey has become one of the strongest critics of Syria's regime. Turkey hosts civilian and military Syrian opposition groups, including hundreds of army defectors who are affiliated with the Free Syrian Army and collect food and other supplies to deliver to comrades on smuggling routes.
Turkish authorities also suspect Damascus, which was collaborating with Turkey in its fight against autonomy-seeking Kurdish rebels, is now turning a blind eye to Syria-based Kurdish fighters who belong to the Kurdistan Workers' Party, or PKK, considered a terrorist organisation in the US and Europe.
The plane, an unarmed F4, went down in the Mediterranean Sea about eight miles from the Syrian town of Latakia, Turkey said. Syria claimed the jet violated its air space over territorial waters, penetrating by about a kilometre. It said Syrian forces only realised it was a Turkish jet after firing at it.
In a telephone interview with Turkish TV news channel A Haber yesterday, Syrian Foreign Ministry spokesman Jihad Makdissi said the downing was "not an attack". "An unidentified object entered our air space and unfortunately as a result it was brought down. It was understood only later that it was a Turkish plane," A Haber quoted Makdissi in a translation of the interview. "There was no hostile act against Turkey whatsoever. It was just an act of defence for our sovereignty."
Turkish President Abdullah Gul conceded the plane may have unintentionally crossed into Syrian airspace, but said such an act was "routine" for jets to unintentionally cross borders for short periods. The government has not described the plane's specific mission.
Mr Gul said his government was still investigating what happened, but "no one should have any doubt that whatever (action) is necessary will be taken".