Syria banned Turkish flights from its airspace on Sunday and Turkey made a similar tit-for-tat move, as regime forces pressed their counter-attack against rebels to regain territory lost in northern battlegrounds.
The reprisal for Turkey confiscating a cargo of what Russia said was radar equipment being flown from Moscow to Damascus came despite a flurry of diplomacy intended to calm soaring tensions between the neighbours.
Syria accuses Turkey of channelling arms from Gulf Arab states to rebels fighting its troops, who have been under mounting pressure across large swathes of the north, including in second city Aleppo.
The Syrian flight ban went into force from midnight (2100 GMT Saturday) "in accordance with the principle of reciprocity", SANA state news agency said.
Turkish Foreign Minister Ahmet Davutoglu said later that Ankara had already banned Syrian civilian flights from its airspace.
"Yesterday (Saturday) we closed our airspace to Syrian civilian flights as we have previously done for Syrian military flights," he said.
"As we have established that civilian flights were being misused by the Syrian defence ministry to transport military material, we sent a note yesterday to the Syrian side," Davutoglu said.
Ankara has taken an increasingly strident line towards its southern neighbour since a shell fired from inside Syria killed five Turks on October 3.
It has since repeatedly hit back for cross-border fire, prompting growing UN concern and a hasty series of diplomatic contacts.
Tensions from the conflict are also being felt in neighbouring Lebanon, and hundreds of people took to the streets of Beirut for two separate rallies, one supporting the Damascus regime and the other calling for its downfall.
With the violence raging, UN and Arab League peace envoy Lakhdar Brahimi on Sunday went to Iran, which handed him an "unofficial detailed proposal" aimed at ending the conflict in its closest ally Syria.
Brahimi, on his second regional tour after taking up his post at the start of September, welcomed the initiative but reiterated a call by UN chief Ban Ki-moon for Damascus to initiate a ceasefire.
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On the battlefield, the military used fighter jets to bombard Maaret al-Numan, captured by the rebel Free Syrian Army earlier in the week, said the Syrian Observatory for Human Rights.
To the east, troops tried to block a new rebel assault on Wadi Deif army base -- the largest in Idlib province, much of which is in rebel hands. Battles erupted nearby as warplanes bombarded the area, said the Observatory.
A military official and the Observatory said troops also recaptured Aleppo's Umayyad mosque two days after rebels claimed control of the site, an important foothold they were hoping to take before surrounding the regime-held citadel.
There was shellfire and rifle shots echoed around the heavily damaged courtyard of the mosque with increasing frequency as regime forces apparently advanced on the mosque, an AFP correspondent reported.
"Quickly, quickly!" one rebel shouted before insurgents sprinted to avoid snipers through a warren of shrapnel-scarred streets filled by dust from the bombardment.
SANA said troops killed and captured "dozens of terrorists and destroyed anti-tank rockets" in the northern city.
In Damascus, two explosions hit the upscale district of Mazzeh early on Sunday, the Observatory said, adding that one targeted the car of a pro-regime lawyer who was critically wounded.
SANA said the other blast was a "suicide attack" that caused no casualties.
In Damascus province, troops took back control of a military base in Atibah, a day after rebels had seized it.
Dozens of corpses were found in a hospital morgue of the province, said the Observatory's Rami Abdel Rahman, adding that they may be of men killed in fighting "over the course of recent months."
At least 130 people including 79 civilians were killed nationwide on Sunday, the Observatory said, in addition to more than 33,000 who have died since the revolt against the regime erupted in March last year.
Human Rights Watch, meanwhile, urged Syria's military to stop using cluster bombs, weapons that can contain up to 650 submunitions which are sprayed over a large area before exploding.
"Syria’s disregard for its civilian population is all too evident in its air campaign, which now apparently includes dropping these deadly cluster bombs into populated areas," said Steve Goose, arms director at the New York-based group.