The Syrian regime rejected a UN call for a unilateral ceasefire on Wednesday as rebels confronted columns of tanks and troops sent to retake a town on the road to main battleground city Aleppo.
Rebels launched an attack on army positions in the northern metropolis's landmark Umayyad Mosque in the heart of the Old City adding to the urgency for the army to restore its supply lines.
Turkey forced a Syrian passenger plane to land in Ankara to check its cargo for weapons and warned its own aircraft to avoid Syrian airspace for fear of retaliation as tensions soared between the two neighbours.
President Bashar al-Assad's regime, on the back foot with rebels controlling swathes of northern Syria, insisted the insurgents must stop the violence first as it turned down the call issued the previous day by UN chief Ban Ki-moon.
"We told Ban Ki-moon to send emissaries to the countries which have influence on the armed groups, so that they put an end to the violence," foreign ministry spokesman Jihad Maqdisi said.
As he spoke, the embattled regime was sending tanks from Mastumah south of Idlib city to Maaret al-Numan, a rebel source told an AFP reporter in the nearby town of Sarmin.
The military also deployed soldiers along the highway to Maaret al-Numan to secure the passage of its heavy armour to the strategic town on the Damascus-Aleppo highway.
The insurgents were battling to halt their advance, however, using rocket launchers and improvised explosive devices, the source said, adding three tanks were damaged.
The intensifying battle for Maaret al-Numan was "very important," said the rebels who took control of the town on Tuesday after 48 hours of fierce fighting and heavy shelling.
In Aleppo, rebels assaulted army positions in the Umayyad Mosque sparking four hours of fighting outside and inside the 13th century place of worship which is one of the landmarks of the city's UNESCO-listed historic heart, a military source said.
"The rebels broke through the wall of the mosque using RPGs (rocket-propelled grenades) and tried to push inside," the source told AFP.
An AFP correspondent reported that the troops had fought off the assault but that rebel snipers were continuing to shoot at army positions from surrounding streets.
Elsewhere in Aleppo, Syria's commercial capital, two mortar rounds struck in front of the central bank building as it was crowded with early morning customers, killing three people outside, a bank clerk told AFP.
Nationwide at least 141 people were killed across Syria on Wednesday, the Syrian Observatory for Human Rights said, among more than 32,000 who have died since the start of the uprising in March last year.
One of those killed was Mohammed al-Ashram, a cameraman who had been working for the pro-government Al-Ikhbariya television channel, which said he was shot dead by "terrorists" in the eastern province of Deir Ezzor.
-- Turkish warning --
The Syrian Airbus A-320 aircraft, which was carrying 35 passengers from Moscow to Damascus, was escorted to Ankara's Esenboga Airport by two Turkish jets, Turkey's Anatolia new agency reported.
"We received information that the plane's cargo did not comply with rules of civil aviation," Turkish Foreign Minister Ahmet Davutoglu was quoted as saying.
Ankara warned Turkish airlines against using Syrian airspace and a plane carrying Turkish pilgrims to the Saudi city of Jeddah landed urgently in the Turkish city of Adana as a precaution, Turkey's NTV television reported.
Russia is a traditionally ally of Assad's regime but it has repeatedly insisted that it will honour only longstanding weapons contracts with Damascus and will provide no new weapons.
Turkey and Gulf states Qatar and Saudi Arabia stand accused by Damascus of supplying weapons to the rebels.
Turkey's top military commander, General Necdet Ozel, warned meanwhile of a tougher response if Syria keeps hitting Turkish soil, as he visited the town of Akcakale, where cross-border shelling killed five civilians last week.
"We have retaliated (for Syrian shelling) and if it continues, we'll respond more strongly," Ozel said, as he inspected Turkish troops on a tour of the heavily fortified border zone.
NATO head Anders Fogh Rasmussen has warned against escalation along the frontier and said the alliance has "all necessary plans in place to protect and to defend Turkey if necessary."