Istanbul — Buoyed by support from his country's NATO allies, Prime Minister Recep Tayyip Erdogan warned Syrian forces on Tuesday to stay clear of their troubled border or face a Turkish military response to any perceived threat, following the disputed downing of a Turkish warplane.
The Turkish leader's bellicose tone came as ambassadors from the NATO alliance, seeking to avoid a wider conflict, held emergency talks in Brussels at Turkey's behest. After the meeting, the NATO secretary general, Anders Fogh Rasmussen, said the alliance considered Syria's actions in shooting down a Turkish warplane last Friday "unacceptable."
In a unanimous statement, the NATO allies called the episode "another example of the Syrian authorities' disregard for international norms, peace and security, and human life." Turkey is a member of the alliance.
"I would certainly expect that such an incident won't happen again," Mr. Rasmussen said at a news conference at NATO headquarters in Brussels. He added that the alliance would closely follow developments and "if necessary, consult and discuss what else could be done."
In Ankara, Mr. Erdogan said Turkey had revised its military rules of engagement toward Syria.
"Every military element that approaches the Turkish border from Syria in a manner that constitutes a security risk or danger would be considered as a threat and would be treated as a military target," he said in a speech to lawmakers attended by Arab diplomats.
"From here, we warn the Syrian regime not to make any mistakes, not to test Turkey's decisiveness and wisdom," Mr. Erdogan said.
"If there is anyone who could not understand this up until today, we would and will prove in the most clear and determined way that Turkey cannot be challenged," he said.
While Syria maintains that the plane was brought down well within its airspace, Turkey says the two-seat F-4 fighter plane was attacked over international waters after straying briefly into Syrian space.
"Our plane was targeted not by mistake but deliberately, entirely in an act of hostility," Mr. Erdogan said. "At a time, place and method defined by itself, Turkey will make use of its rights that derive from international law and firmly take necessary steps against this injustice." He did not elaborate on what those steps might be.
Turkey and Syria share strong historical and cultural ties, and were both ruled by the Ottoman Empire for centuries, until the empire collapsed and the modern Turkish Republic was founded almost 90 years ago. Before the Syrian revolt broke out in 2011, Mr. Edrogan had pursued a strong regional friendship with President Bashar al-Assad of Syria, but there was no trace of that warmth in Mr. Erdogan's address on Tuesday.
Since then, the 550-mile border has become a critical fault line and potential flash point, used by an increasingly sophisticated network of activists in southern Turkey smuggling crucial supplies into Syria including weapons, communications gear, field hospitals and even salaries for soldiers who defect.
At the same, it has offered escape routes to tens of thousands of fugitive Syrian civilians and to increasingly high-ranking military defectors, the most recent on Sunday.
Turkey's role in support of the rebels, thus, has cast it as a frontline in the regional struggle for Syria's future.
"We will continue to support the struggle of our Syrian brothers at all costs," Mr. Erdogan said on Tuesday said, referring to the opponents of Mr. Assad. "We will continue to act in solidarity with our brothers until the Syrian people are freed of this cruel dictator," he said.
The Turkish foreign minister, Ahmet Davutoglu, has told state-owned TRT television that the aircraft was struck by antiaircraft fire outside of Syrian airspace. "Our plane was hit in international airspace, 13 nautical miles out of Syria, when Syrian territorial space is 12 miles," he said.
But the Syrian Foreign Ministry said on Monday that the airplane was brought down by an antiaircraft weapon with a range of less than two miles.
The two crewmen are still missing.
Western defense analysts said the episode had shown that, unlike the example of Libya last year, when NATO planes enforced a no-fly zone as rebels pressed for the ouster of Col. Muammar el-Qaddafi, the Syrian military could offer much stiffer resistance.
"After its experience in Libya, NATO certainly does not want to get into another air war with the Syrians, who are in much better shape than the Libyans were to conduct one," said Michael Corgan, a specialist in international security issues at Boston University.
In calling for the meeting in Brussels on Tuesday, Turkey said it was invoking Article 4 of the NATO treaty, which provides for consultations by the allies when one of them is attacked or threatened, rather than the much stronger Article 5, in which an attack on one member is considered an attack on all NATO countries.
Russia, with Chinese support, has shielded President Bashar al-Assad against the efforts of Western and some Arab nations to press for a settlement that would remove the Syrian leader from office as part of a transition.
The nature of the weapons system that brought down the Turkish plane has not been clearly established.
Less than two weeks ago, by apparent coincidence, Russia's main arms exporter said it was supplying Syria with defensive missile systems that could bring down airplanes or sink ships.
"I would like to say these mechanisms are really a good means of defense, a reliable defense against attacks from the air or sea," Anatoly P. Isaykin, the general director of the company, Rosoboronexport, said Friday in an interview. "This is not a threat, but whoever is planning an attack should think about this."
On Monday, Jihad Makdissi, the Syrian Foreign Ministry spokesman, claimed that the wreckage of the downed Turkish jet "shows holes in the tail-end of the plane which confirm that it was shot down by a ground-based machine gun, not missiles."
"Had the aircraft been over territorial waters, we would have used missiles, not a land-based antiaircraft machine gun with a maximum range of 2.5 kilometers," he said. "All of this confirms the falsity of the allegations that the aircraft was shot down outside Syrian territorial waters."
The source of the spokesman's version was not immediately clear. It contradicted accounts offered by Turkey, which has said the wreckage of the plane is lying in deep water far offshore and has yet to be recovered. Indeed, on Monday, Turkey accused Syria of firing on a reconnaissance plane that was searching for the wreckage.
In an unusually detailed account on the SANA Web site, Mr. Makdissi claimed that coastal antiaircraft artillery stationed on Syrian beaches opened fire on the Turkish jet as it flew toward the Syrian coast at a speed of some 500 miles an hour. The airplane was flying very low over the Mediterranean Sea, Mr. Makdissi said, and dipped below the reach of radar, "only to appear suddenly at an altitude of 100 meters, one to two kilometers from the beach and Syrian land, and became suddenly visible to the naked eye."
After it was hit, the plane veered to the left and crashed, he said.