ANKARA, Turkey – Syria said Saturday it 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 signaled that the violence gripping Syria is increasingly bleeding outside its borders.

Syria and neighboring 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 that Damascus, which was collaborating with Turkey in its fight against autonomy-seeking Kurdish rebels, is now turning a blind eye to Kurdish fighters in Syria who belong to the Kurdistan Workers’ Party, or PKK, considered a terrorist organization in the U.S. and Europe.

The plane, an unarmed F-4, 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 more than a half mile. It said Syrian forces only realized it was a Turkish jet after firing at it.

In a telephone interview with Turkish TV news channel A Haber on Saturday, Syrian Foreign Ministry spokesman Jihad Makdissi said the downing was “not an attack.”

“There was no hostile act against Turkey whatsoever. It was just an act of defense for our sovereignty,” A Haber quoted Makdissi in a translation of the interview.

Turkish President Abdullah Gul conceded the plane may have unintentionally crossed into Syrian airspace, but he 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.

Gul said his government was still investigating what happened but that “no one should have any doubt that whatever (action) is necessary will be taken.”

It was not clear whether that action would involve military retaliation, increased sanctions or other steps, including demands for compensation or an apology.

Germany and Iraq urged the countries to remain calm and not let the unrest in Syria become a wider conflict,

“Our main concern is the spillover of the crisis into neighborhood countries. No country is immune from this spillover,” Iraq Foreign Minister Hoshyar Zebari said.