Syrian rebels trying to fight off an army offensive in Aleppo said on Tuesday they were running low on ammunition as President Bashar al-Assad's forces encircled their stronghold at the southern entrance to the country's biggest city.
Mr Assad, dealt another political blow on Monday with the defection of his prime minister, has reinforced his troops in preparation for an assault to recapture rebel-held districts of Aleppo after repelling fighters from most of Damascus.
"The Syrian army is trying to encircle us from two sides of Salaheddine," said Sheikh Tawfiq, one of the rebel commanders, referring to the southwestern neighbourhood which has seen heavy fighting over the last week.
Mortar fire and tank shells exploded across the district early on Tuesday, forcing rebel fighters to take cover in crumbling buildings and rubble-strewn alleyways.
Tanks have entered parts of Salaheddine and army snipers, using the cover of heavy bombardment, deployed on rooftops, hindering rebel movements.
Another rebel commander, Abu Ali, said snipers at the main Saleheddine roundabout were preventing the rebels from bringing in reinforcements and supplies. He said five of his fighters were killed on Monday and 20 wounded.
But rebels said they were still holding the main streets of Salaheddine which have been the frontline of their clashes with Assad's forces.
A fighter jet pounded targets in the eastern districts of Aleppo and artillery shelling could be heard in the early morning, an activist in Aleppo said.
"Two families, about 14 people in total, were believed killed when a shell hit their home and it collapsed this morning," the activist said. The house was one street away from a school being used by rebels, he said.
As Assad's forces battle to retake Aleppo, the president has suffered a series of setbacks including on Monday when Prime Minister Riyad Hijab denounced the "terrorist regime" in Damascus after fleeing the country.
The defection of Mr Hijab, who like most of the opposition hails from the Sunni Muslim majority, was a further sign of the isolation of Assad's government around an inner core of powerful members of his minority Alawite sect.
Opposition figures, buoyant despite setbacks in recent weeks of fighting in the two main cities Damascus and Aleppo, spoke of an extensive and long-planned operation to spirit Hijab and his large extended family across the border to Jordan.
"I announce today my defection from the killing and terrorist regime and I announce that I have joined the ranks of the freedom and dignity revolution," Hijab said in a statement read by a spokesman on Al Jazeera television. He declared himself "a soldier in this blessed revolution".
A spokesman for US President Barack Obama hailed Mr Hijab's defection as a sign that the 40-year rule of Mr Assad's family was "crumbling from within" and said he should step down.
Western leaders' repeated predictions of Mr Assad's imminent collapse have so far proven premature, however.
The security forces have overwhelming superiority in firepower, which they have wielded against lightly armed rebels.
The rebels gathered momentum last month, attempting to seize Damascus and Aleppo after an audacious bomb attack killed four members of Assad's inner circle. But the government counteroffensive has been devastating, with troops largely recapturing Damascus and using helicopters and tanks to hammer rebels who still control parts of Aleppo.
The war has increasingly divided the region along its sectarian faultline, pitting the mainly-Sunni rebels, who are backed by regional Sunni-led powers Turkey and the Gulf Arab states, against a government that is backed by Shi'ite Iran.
State news agency SANA said Mr Assad met the secretary of Iran's Supreme National Security Council, Saeed Jalili, on Tuesday. It gave no details.
Iran has expressed worry about the fate of more than 40 Iranians it says are religious pilgrims kidnapped by rebels off a bus in Damascus while visiting Shi'ite shrines.
The rebels say they suspect the captives were troops sent to help Mr Assad. A rebel spokesman in the Damascus area said on Monday three of the Iranians had been killed by government shelling, and the rest would be executed if the shelling did not stop.
Mr Hijab's defection was the latest sign of Sunnis abandoning Mr Assad, but there has been no sign yet that members of his mainly Alawite ruling inner circle are losing their will to fight on.
"Defections are occurring in all components of the regime save its hard inner core, which for now has given no signs of fracturing," said Peter Harling at the International Crisis Group think-tank.
"For months the regime has been eroding and shedding its outer layers, while rebuilding itself around a large, diehard fighting force," he said. "The regime as we knew it is certainly much weakened, but the question remains of how to deal with what it has become."
© Thomson Reuters 2012