22 June 2012 Last updated at 12:31 ETThe Turkish military said it lost radio contact with the F-4 while it was flying over Hatay
Turkey's government has called an emergency security meeting amid reports that one of its fighter jets was shot down by Syrian security forces.
The Turkish military earlier said it had lost contact with an F-4 Phantom over the Mediterranean Sea on Friday morning, south-west of Hatay province.
It did not confirm reports that Syrian air defence forces were responsible.
But local media are quoting Prime Minister Recep Tayyip Erdogan as saying "the other side have expressed regret".
Mr Erdogan also revealed that the two crew members were safe.
Relations between Turkey and Syria, once close allies, have deteriorated sharply since the uprising against Syrian President Bashar al-Assad began in March 2011.
'Syrian waters'The Turkish military said it lost radio contact with the F-4 at 1158 (0858 GMT) on Friday while it was flying over Hatay, about 90 minutes after it took off from Erhac airbase in the province of Malatya, to the north-west.
"Search-and-rescue efforts have started immediately," a statement said.
The private news channel, NTV, later cited unnamed military sources as saying that the plane had crashed off Hatay's Mediterranean coast, in Syrian territorial waters, but that there had been no border violation.
The Turkish and Syrian coast guards were collaborating in the search for the two crew members and the plane, NTV reported.
Witnesses in the Syrian coastal city of Latakia meanwhile told BBC Arabic that Syrian air defences had shot down an unidentified aircraft near the town of Ras al-Basit.
Lebanon's al-Manar television channel - controlled by Lebanon's Hezbollah Shia movement, an ally of the Syrian government - also reported that Syrian security sources had said that "Syrian air defences shot down a Turkish warplane and hit another in Syrian airspace".
There was no immediate confirmation from Turkish officials, but later it was announced that Mr Erdogan would be holding an emergency meeting with his top military and intelligence chiefs to discuss the missing plane.
Mr Erdogan was also said to have told Turkish reporters on a flight back from Brazil that "the other side have expressed regret" over the downing of the F-4, and also that the pilots had been recovered.