Turkish Prime Minister Tayyip Erdogan told Syria to beware the wrath of Turkey after the shooting down of a warplane and said he had ordered the armed forces to react to any military threat from Syria near the two countries' border.
Erdogan's warning to Syria reflected increased tensions not only on the Mediterranean coast, where the aircraft was shot down last Friday, but on a long common land border criss-crossed by rebels fighting President Bashar al-Assad.
Syria said on Sunday it had killed several "terrorists" infiltrating from Turkey.
In Syria itself, Damascus suburbs were gripped by the worst fighting in the capital since the uprising against Assad began 16 months ago. The city had long been seen as a bastion of support for the president.
Erdogan, who fell out with Assad after he dismissed his advice to allow reforms, said Turkey was no warmonger.
"Our rational response should not be perceived as weakness, our mild manners do not mean we are a tame lamb," he told a meeting of his parliamentary party. "Everybody should know that Turkey's wrath is just as strong and devastating as its friendship is valuable."
NATO member states, summoned by Turkey to an urgent meeting in Brussels, condemned Syria over the incident that resulted in the loss of two airmen. The cautious wording of a statement demonstrated the fear of Western powers as well as Turkey that armed intervention in Syria could stir a sectarian conflict across the region.
"Those who want war may be disappointed by the prime minister's speech," Turkish journalist Mehmet Ali Birand wrote on social media. "But a big part of society breathed a sigh of relief."
Erdogan said the armed forces' rules of engagement had been changed as a result of the attack, which Turkey says took place without warning in international air space.
"Every military element approaching Turkey from the Syrian border and representing a security risk and danger will be assessed as a military threat and will be treated as a military target," he said.
Turkey is the base for the rebel Free Syrian Army (FSA) and shelters more than 30,000 refugees - a number Erdogan worries could rise sharply as fighting spreads. Rebel soldiers move regularly across the border and defectors muster inside Turkey.
Fighting has often moved very close to the frontier and could under the new rules of engagement draw Turkish military reaction, especially if Syrian forces pursue rebels.
Rebels and pro-Assad forces now clash daily across Syria. Fighting broke out in the suburbs of Damascus on Tuesday, activists said.
Video posted by activists showed heavy gunfire and explosions. Blood pooled on a pavement in Qudsiya suburb and a blood trail led to a building to where one casualty had been dragged. A naked man writhed, his body pierced by shrapnel.
The Syrian state news agency SANA said insurgents had blocked the old road from Damascus to Beirut.
Dozens of them were killed or wounded and others arrested it said. Government forces also seized rocket launchers, sniper rifles, machineguns and a huge amount of ammunition, it said.
Syrian and Turkish accounts of Friday's plane shoot down differed.
Syria says it had no choice but to take out the plane as it entered Syrian air space flying low and at high speed. It found out it was Turkish only after the engagement. Turkey insists its aircraft entered Syrian air space only briefly by mistake.
Erdogan said Syrian military helicopters had violated Turkish airspace five times this year without Turkey firing on them. He saw Friday's attack as a deliberate attack.
"Our plane was targeted on purpose, and in a hostile way, not as a result of a mistake. The attitude of the Syrian officials following the incident is the most concrete evidence that our jet was attacked on purpose."
According to Turkey, the Phantom jet was testing Turkish air defenses near the countries' common maritime border when it was shot down. Some analysts say it might also have been probing Syria's Russian-supplied radar and air defenses that would be an obstacle to any form of Western military involvement in Syria.
Russia, which has opposed Western calls for Assad's removal, said the shoot down should not been seen as a provocation or a premeditated action.
Moscow has close relations with Damascus and has a naval base at Syria's port city of Tartus close to the spot where the jet was downed.
Moscow-based defense think-tank CAST said Russia was expected to deliver nearly half a billion dollars worth of air defense systems, repaired helicopters and fighter jets to Syria this year despite international pressure to halt the arms sales.
Russia said it was crucial that Iran should also attend a meeting on Syria of the five permanent U.N. Security Council members and regional players being organized by international mediator Kofi Annan in Geneva this weekend.
Western countries oppose Iran, Syria's closest regional ally, taking part in the meeting and some diplomats have said it was not entirely clear whether it would take place.
Friday's incident is unlikely to increase Turkey's appetite for an intervention it fears would have unpredictable consequences for itself and for a region riven by sectarian division. But it has in the past spoken of the possibility of creating humanitarian corridors inside Syria.
"For Turkey there are two bad scenarios: one, a mass influx of refugees and two, large-scale massacres in Syria," said a Turkish official who declined to be named.
"Ankara has not taken a decision for military intervention or a humanitarian corridor at the moment. But if these are needed, everybody would prefer that they will be done with international legitimacy. However, if things go really badly we have to be ready for any kind of eventuality," he added.