Syria army attacks Aleppo as tanks move in

Syrian army tanks around Aleppo have begun moving in on south-western districts of the city, activists say.

They say the bombardment of rebel-held areas intensified in the early morning, with military aircraft overflying the city at low altitudes.

The BBC's Ian Pannell, in Aleppo, says many casualties have been reported and families are fleeing.

Western nations have warned of a potential massacre in Aleppo, Syria's most populous city.

Syrian state television said that rebels, having failed in Damascus, were now trying to turn Aleppo into a den for their terrorism.

According to the opposition Local Co-ordination Committees, a network of activists, the much-anticipated government offensive has begun.

From first light, the sound of a heavy artillery bombardment reverberated across this city. The rebels say tanks and armoured vehicles have started to advance towards Salah al-Din, one of the most restive neighbourhoods in Aleppo, where they have apparently met fierce resistance.

Many casualties are being reported and an emergency call has gone out to doctors to help. Pro-government forces are said to have entered another area too, and the sound of heavy skirmishing can be heard all around.

Cars and trucks packed with families are heading out to the countryside, fearing there will be a massacre in the city. Both sides are determined to control this place, but the overwhelming firepower belongs to President Assad's men, and they are prepared to use it to retake Aleppo.

The rebels say they have destroyed a number of tanks, but their claim cannot be independently verified.

Our correspondent says the rebels are vastly outgunned and outmanned by forces loyal to Syrian President Bashar al-Assad.

Activists have reported violent clashes around the Salah al-Din and Hamdanieh quarters near the centre of Aleppo.

An emergency call has gone out to doctors to come to Salah al-Din and help if they can, our correspondent says.

On Friday, the Red Crescent suspended some of its operations in Aleppo because of the heavy fighting.

Rebels had been stockpiling ammunition and medical supplies in preparation for the expected assault.

The fighting comes after two weeks during which rebels made significant gains.

On 18 July, an attack at Syrian security headquarters in Damascus killed four senior officials, including the defence minister and President Bashar al-Assad's brother-in-law.

Rebels took control of several parts of Damascus before being driven out by a government counter-offensive.

The rebels also seized several border crossings with Turkey and Iraq.

There has been fighting around Aleppo for the past week, with the government deploying fighter jets and helicopter gunships to beat back the rebels.

Until recently, Aleppo and Damascus had been relatively free of the violence that has wracked other parts of the country.

Earlier this week, thousands of government forces were moved from the border with Turkey to join fierce fighting in Aleppo, activists said.