Fierce fighting rocks Syria's Aleppo

Fierce fighting rocked the heart of Syria's commercial capital Aleppo early as troops shelled rebel-held districts in the east of the key battleground city, a human rights group said.

Fierce fighting rocked the heart of Syria's commercial capital Aleppo early on Tuesday as troops shelled rebel-held districts in the east of the key battleground city, a human rights group said.

The clashes came after at least 265 people were killed in violence nationwide on Monday, 182 of them civilians, the Syrian Observatory for Human Rights said, revising sharply upwards an earlier toll.

The figure made Monday one of the deadliest days since the outbreak of the uprising against President Bashar al-Assad's rule in March last year, the Britain-based watchdog said.

Troops fought with rebel fighters in the Bab Antakya, Aziziyeh, Bab Janin and Sabaa Bahrat areas of central Aleppo and near the Palace of Justice in the west, the Observatory said.

Fighting broke out for the first time in the Ashrafiyeh district in the northwest, the watchdog's director Rami Abdel Rahman told AFP. "Clashes broke out there after rebels attacked a military post," he said.

Aleppo has been bracing for a threatened ground offensive by the army against the rebels, who say they control around half of the city.

A senior security official said on Sunday that the army had completed the build-up of some 20,000 troops in readiness for a decisive showdown in the battle under way since July 20.

Troops shelled rebel-held neighbourhoods in the east of the city, the Observatory said. Opposition activists of the Syrian Revolution General Commission said the army used helicopter gunships in its pounding of the Hanano district.

The head of the UN observer mission in Syria, Lieutenant General Babacar Gaye expressed concern for civilians trapped in the fighting in the city of some 2.7 million people.

Fighting in Aleppo killed 57 people on Monday alone, the majority of them civilians, the Observatory said.

"I urge the parties to protect civilians and respect their obligations under international humanitarian law," Gaye said in a statement on Monday. "Civilians must not be subjected to shelling and use of heavy weapons."

Approximately 20 unarmed UN observers were moved out of Aleppo back to the mission's Damascus headquarters at the weekend because of worsening security, a UN spokeswoman said.

Nationwide, 21 rebel fighters and 62 security force personnel were also among Monday's dead, according to the Observatory's revised toll.