BEIRUT, Lebanon — Turkey announced Friday that Syrian forces had shot down a Turkish warplane with two crew members over the Mediterranean, a potentially ominous turn for the worse in relations already frayed because of Turkey’s support for Syrian rebels fighting to overthrow President Bashar al-Assad.

The Syrians later acknowledged their antiaircraft gunners had downed the plane, contending it had violated Syrian airspace.

Turkey’s announcement, from the office of Prime Minister Recep Tayyip Erdogan, came after an emergency security meeting by Turkish officials in Ankara over the fate of the plane, which had been reported missing hours earlier amid conflicting reports over whether it had crashed or had been downed intentionally.

The measured wording of the announcement suggested that Turkey had not yet concluded that the Syrian action was provocative, and it acknowledged that Syrian rescue teams were cooperating in trying to locate the aircraft and crew. But the statement also left open the possibility that Turkey, a NATO member, would respond militarily, an outcome that could further complicate and widen the Syrian conflict.