A Turkish fighter jet shot down a Syrian military helicopter on Monday after it entered Turkish airspace and ignored repeated warnings to leave, an official said.
The helicopter strayed more than a mile into Turkish airspace, but crashed inside Syria after being hit by missiles fired from the jet, Turkey's deputy prime minister, Bulent Arinc, told reporters in Ankara.
Arinc said he did not have any information on the fate of the Syrian pilots, but Rami Abdul-Rahman, director of the Syrian Observatory for Human Rights, said rebel fighters captured one of the pilots, while the fate of the other one was unclear.
The incident is bound to ramp up tension on an already volatile border. Turkey has been at odds with the Syrian government since early in the country's civil war and has backed the Syrian rebels, while advocating international intervention in the conflict.
Turkish Foreign Minister Ahmet Davutoglu, speaking in Paris after meetings about Syria with his counterparts from other countries, said Monday's encounter should send a message. "Nobody will dare to violate Turkey's borders in any way again," he said, according to Anatolia, the Turkish state-run news agency. "The necessary measures have been taken."
He said details of the incident would be provided to U.N. Secretary-General Ban Ki-moon and the U.N. Security Council and fellow members of the NATO military alliance.
Arinc noted that the Turkish military had put its forces on a higher state of alert and changed the rules for engaging with the Syrian military along the border because of "constant harassment fire from the other side."
He also noted that a Turkish jet was shot down by Syrian anti-aircraft over the Mediterranean in June 2012. Turkey says it was hit in international airspace, but Syria insisted it was flying low inside Syrian airspace.
Shells from the Syrian conflict have occasionally rained down on the Turkish side of the border, and Turkish Prime Minister Recep Tayyip Erdogan has warned Damascus that his country would not tolerate any violation of the border by Syrian forces.
Turkey, one of Syrian President Bashar al-Assad's fiercest critics, has advocated military intervention in Syria and grown frustrated over what it sees as Western indecisiveness.
It shares a 560-mile border with Syria and is sheltering a quarter of the 2 million people who have fled the Syrian conflict.
Turkey has bolstered its defenses and deployed additional troops on its southeastern border in recent weeks, with convoys of military vehicles ferrying equipment and personnel and additional short-range air defenses set up.
Its armed forces have frequently responded in kind to stray gunfire and mortar rounds hitting its territory and it is hosting six NATO Patriot missile batteries meant to defend it against any attacks from Syria.