Syria banned Turkish passenger flights from its airspace from Sunday in a retaliatory move after Turkey confiscated a cargo of what Russia said was radar equipment en route from Moscow to Damascus last week.
The reprisal, just weeks before the annual hajj when thousands of Turkish pilgrims head to the Muslim holy places in Saudi Arabia on a route that would normally take them through Syrian airspace, came despite a flurry of diplomacy on Saturday intended to calm soaring tensions between the neighbours.
Syria accuses Turkey of channeling arms from Gulf Arab states to rebels fighting its troops, who have been under mounting pressure across large swathes of the north, including second city Aleppo.
The flight ban went into force from midnight (2100 GMT Saturday) "in accordance with the principle of reciprocity", SANA state news agency said, although Turkey has said its airspace remains open to Syrian civilian flights.
Since last Wednesday, Turkey had warned its airlines to avoid Syrian airspace for fear of retaliation for that day's interception of the Syrian Air flight by Turkish jets on the allegation it was carrying military equipment.
The United States backed its NATO ally's confiscation of what Russia said was radar spare parts, saying they constituted "serious military equipment".
Russia, traditional ally of President Bashar al-Assad's regime, insisted the cargo broke no international rules.
Turkey has taken an increasingly strident line towards its southern neighbour since a shell fired from the Syrian side of the border killed five of its nationals on October 3.
It has since repeatedly retaliated for cross-border fire, prompting growing UN concern and a flurry of diplomatic contacts.
After talks with his German counterpart Guido Westerwelle on Saturday, Turkish Foreign Minister Ahmet Davutoglu reiterated that Ankara would not tolerate any further border incidents.
"We will hit back without hesitation if we believe Turkey's national security is in danger," he said.
Westerwelle renewed Germany's support for its NATO ally while at the same time appealing for restraint. "We are on Turkey's side but we also call on Turkey to show moderation," he said.
Peace envoy Lakhdar Brahimi, a veteran Algerian diplomat who is the envoy of the United Nations and the Arab League, headed to Iran, the Syria government's closest ally, after holding talks in Saudi Arabia and Turkey, the leading backers of the opposition.
Brahimi is on his second tour of the region after taking up his post at the beginning of September, replacing former UN chief Kofi Annan who quit complaining that he had not received sufficient support from the major powers to see through his abortive April peace plan.
On the ground, fierce fighting raged between the army and rebel fighters on the main highway between Damascus and Aleppo.
The rebels' capture of the strategic crossroads town of Maaret al-Numan last Tuesday has threatened the army's ability to reinforce its beleaguered troops in the northern metropolis.
One rebel fighter was killed and 18 wounded as fighting raged for a second day around the nearby Wadi Daif base, which remains in government hands, the Syrian Observatory for Human Right said.
Air strikes targeted the rebels in the village of Marshurin and in Hish in the same region, the Britain-based watchdog added.
The clashes came after fierce fighting in the heart of Aleppo on Saturday which saw rebels attack army positions inside the city's landmark Umayyad Mosque for the second time in a week.
The commercial capital has been the key battleground of the 19-month conflict since mid-July.
Its ancient covered market or souk has also been damaged in the fighting as rebels and troops have exchanged mortar and grenade fire in the UNESCO-listed Old City.
Rebels entered the mosque complex by planting an explosive device at the southern entrance,
Nationwide at least 181 people were killed on Saturday -- 71 civilians, 63 soldiers and 47 rebels, according to the Observatory's figures.
More than 33,000 people have now been killed since the uprising against Assad's rule erupted in March last year, the watchdog says.
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