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.