BEIRUT — Syria's isolation deepened Monday, hit by a rash of high-ranking military defectors who sought refuge in Turkey, new sanctions and plans for an emergency NATO meeting over its shooting down of a Turkish warplane.

In a new twist, Deputy Prime Minister Bulent Arinc of Turkey also accused the Syrians of shooting at a second Turkish plane — a search-and-rescue aircraft deployed to look for the downed warplane when it was hit Friday off the Mediterranean coast, Turkey's Anatolian News Agency reported.

Arinc did not specify where that incident happened or whether the second plane was hit, but that Turkish officials had contacted the Syrians afterward and "this assault was immediately halted."

There was no immediate comment from Syria to that accusation. But earlier Monday, seeking to publicly justify the shooting of the warplane and to profess no ill will toward Turkey despite rising tensions between the neighbors, the Foreign Ministry's spokesman told reporters in Damascus that the warplane had violated Syria's territory.

"We had to react immediately," said the spokesman, Jihad Makdissi. "Even if the plane was Syrian we would have shot it down."

Turkey says the warplane was over international waters when it was shot down after straying briefly into Syrian airspace.

Makdissi's comments came a day before emergency talks at NATO headquarters in Brussels over the episode, which has heightened regional tensions springing from the 16-month crackdown on the anti-government uprising in Syria. In Luxembourg, the European Union renewed its condemnation of the violence in Syria and tightened its sanctions on the Syrian regime another notch, targeting "banking, military and state media entities," Foreign Secretary William Hague of Britain said.

"We have also decided to strengthen the arms embargo so that the insurance and reinsurance of arms shipments is explicitly prohibited," he said after a meeting of EU foreign ministers.

Last week, a British insurer canceled coverage of a Russian freighter carrying helicopters and anti-aircraft weapons to Syria.

The Turkish foreign minister, Ahmet Davutoglu, said in a Twitter message posted from his official account Sunday that Turkey, a NATO member, would invoke Article 4 of the NATO treaty, which provides for consultations by the allies when one of them is attacked or threatened. He did not cite the much-stronger Article 5, in which an attack on one member is considered an attack on all NATO countries and obliges a concerted response.

Davutoglu posted the messages after he told state-owned TRT television that the Turkish authorities' analysis of radar, visual and communications data had confirmed that their aircraft was struck by Syrian anti-aircraft weapons 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.

He said the Turkish investigation had left no doubt that the aircraft, a two-seat F-4 Phantom, had briefly strayed over Syria but had been shot down after leaving its territory.

Syria disputed that account Monday, with Makdissi saying the plane was brought down by a surface-to-air weapon with a range of less than two miles.

Turkey is a major regional player, but its relations with neighboring Syria have worsened over the months of bloodletting, during which the country has sided with those Western and Arab powers seeking the ouster of President Bashar Assad.

It has also become a haven for defecting Syrian officers. A government official said Monday that a general and two colonels along with lower-ranking soldiers with their families crossed into Turkey late Sunday. More than a dozen Syrian generals have been reported seeking refuge in Turkey as the bloodletting in their own land has intensified. Last week, Jordan said it had granted asylum to a Syrian air force colonel who defected piloting a MiG warplane. Overall, some 33,000 Syrians have sought refuge in Turkey after the Syrian uprising.