The Syrian army today launched a ground assault on the northern city of Aleppo, a Syrian security official told AFP.

"The army is advancing from west to east to cut Salaheddin in half horizontally," the official said on condition of anonymity, referring to the key rebel stronghold in the city.

"It will not take a long time to control the district, even if there are some pockets of resistance remaining," the source added.

A rebel commander confirmed that army tanks had penetrated Salaheddin on Wednesday morning, sparking fierce clashes with the insurgents.

"The regime forces advanced into Al-Malaab Street with tanks and armoured vehicles and fierce fighting is now taking place in the area," said Wassel Ayub, a commander in the rebel Free Syrian Army.

When asked how far the government forces had reached, the defected Syrian army captain said that "the army is present in less than 15 percent of Salaheddin."

The army, which has been massing its troops and armour in and around Aleppo since late last month, was moving from west to east, coming from Hamdaniyeh, a district adjacent to Salaheddin, Ayub added.

The Syrian Observatory for Human Rights, for its part, said that the clashes taking place in streets of Salaheddin and in surrounding areas were the most fierce that Aleppo has seen in the nearly 17-month uprising.

On Sunday, the Syrian security source said that the army had completed the buildup of some 20,000 troops in readiness for a decisive showdown in the battle for the country's economic hub, underway since July 20.