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.
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.
It had 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.
Rebels also intercepted troops on the outskirts of Khan Sheikhun, south of Maaret al-Numan, where intense clashes erupted even as warplanes bombed rebel zones, the Syrian Observatory for Human Rights said.
"If the rebels, who already have Maaret al-Numan and Saraqeb, take Khan Sheikhun, they will completely isolate regime troops in Aleppo because redeployments will not be able to arrive," Observatory director Rami Abdel Rahman said.
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," General Ozel said, as he inspected Turkish troops on a tour of the heavily fortified border zone.
Following the deadly shelling in Akcakale on Wednesday of last week, Turkey's parliament approved the use of military force if necessary against Syria.
Prime Minister Recep Tayyip Erdogan has also warned Damascus not to test Turkey's patience.
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."
The sabre-rattling added to growing fears of wider regional fallout from the conflict ravaging Syria, in which activists say more than 32,000 people have died, mostly civilians.
Separately, Jordan's army denied the US military was helping the kingdom handle an influx of Syrian refugees and prepare for other scenarios, including Damascus losing control of its chemical weapons.
A senior US defence official said earlier that a 150-strong force of planners and specialists – led by a US officer – was looking at ways to prevent the increasingly bloody war from spilling across Jordan's borders.
Residents of the Old City neighbourhood of Homs, meanwhile, desperately pleaded for assistance as the Observatory reported heavy shelling of rebel belts across the central city and nearby Qusayr, both besieged for months.
The army has vowed to overrun the whole of Homs province by the end of the week to free up troops for northern battle zones like Aleppo, and the latest offensive has prompted hundreds of civilians to flee to neighbouring Lebanon.
An activist speaking to AFP over the Internet from Homs said the Old City district was "totally surrounded."
"There is no way out. Our situation is so bad it makes anyone cry," said Abu Bilal. "The field hospitals are full of injured people needing operations and who need to be evacuated. There is no way out at all."
The Observatory also reported heavy shelling on Wednesday against a string of rebel-held neighbourhoods in Aleppo, which has been the theatre since mid-July of an increasingly bloody battle between rebels and the army.
The Britain-based group reported at least 50 people killed across Syria on Wednesday - 18 rebels, 16 soldiers and 16 civilians.
One of the civilians 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.