WASHINGTON — Buoyed by support from its NATO allies, Turkey escalated its warnings against Syria on Tuesday, even as some American and allied officials privately raised questions about whether the Turkish warplane shot down by Syrian air defenses — provoking the denunciation — had been on a spy mission.
In response to the downing, Prime Minister Recep Tayyip Erdogan of Turkey warned Syrian forces to stay clear of their troubled border or face a military response to any perceived threat. Mr. Erdogan’s bellicose tone came as ambassadors from the Atlantic 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 the Turkish warplane to be “unacceptable.”
While the American and allied officials emphasized that some intelligence reports flowing in since the downing last Friday were murky and often conflicting, they said a preliminary analysis of the available data suggested that there may have been more to the aircraft’s mission than just a routine training exercise to test Turkey’s air defenses.
They pointed to several unanswered questions about the episode, including why, given the tensions between the two countries, Turkey was flying an unarmed reconnaissance plane so close to the Syrian border, where the aircraft was struck, and whether it had received any warnings to leave Syrian airspace.
Syria maintains that the plane was brought down by antiaircraft fire well within its airspace. But Turkey says the plane was attacked over international waters after straying briefly into Syrian space.
American military and NATO officials said they were examining these claims as well as radar tracks and other classified information to better understand what had happened.
But the officials said they were loath to publicly challenge an ally’s version of the downing, which the White House and the State Department have condemned as unjustified and have cited as an example of the recklessness of the security forces loyal to President Bashar al-Assad of Syria.
“On a political level, NATO is taking the Turks at their word,” said a senior United States official who has reviewed classified reports of the episode.
One senior NATO diplomat said that even if the Turks were spying on Syria’s military readiness, it should not alter the international reaction. “When this happens between neighboring countries, you give a warning and then send up interceptors,” said the official, who was not authorized to speak on the record. “You don’t just shoot down the plane.”
Turkey’s deputy prime minister, Bulent Arinc, acknowledged on Monday that the aircraft — a two-seat RF-4E Phantom, an unarmed reconnaissance version of the F-4 fighter jet — was equipped for surveillance. But he strongly denied it was doing reconnaissance on this particular mission. The RF-4E has the ability to gather high-resolution imagery about 60 miles from the target, aviation experts said.
“If it had had a reconnaissance mission as claimed, our plane should have been accompanied by other warplanes for security purposes and the maneuvers required as part of such a mission could have been clearly seen on the radar screens,” Mr. Arinc said on Monday, as quoted by the semiofficial Anatolian News Agency.
That assertion, however, did not dispel doubts among officials here, in allied capitals and even in the blogosphere, that the training exercise also included some reconnaissance.
“Was the RF-4E shot down off Syria flying a mission to probe the Damascus air defense system similar to those flown (quite regularly) in the Aegean Sea to probe Greece’s air defenses?” the Aviationist, a blog that follows military and civilian aviation, asked on Tuesday. The two countries have given sharply differing accounts of the downing.
The Turkish foreign minister, Ahmet Davutoglu, has told state-owned TRT television that the aircraft was struck by antiaircraft fire outside Syrian airspace. “Our plane was hit in international airspace,” he said, “13 nautical miles out of Syria, when Syrian territorial space is 12 miles.”
But the Syrian Foreign Ministry said on Monday that the plane was brought down by an antiaircraft weapon with a range of less than two miles. The two crewmen are still missing.
The nature of the weapons system that brought down the plane has also not been clearly established.
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 in deep water far offshore and has yet to be recovered. 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 said 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.
At their meeting in Brussels, the NATO allies, in a unanimous statement, called the episode “another example of the Syrian authorities’ disregard for international norms, peace and security, and human life.”
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.
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 Assad, but there was no trace of that warmth in Mr. Erdogan’s address on Tuesday.
The 550-mile border that the two nations share has become a critical fault line, 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.
Eric Schmitt reported from Washington, and Sebnem Arsu from Istanbul. Alan Cowell contributed reporting from Paris, Paul Geitner from Brussels, and Rod Nordland from Beirut, Lebanon.