Members of the Free Syrian Army chant slogans against Syrian President Bashar al-Assad in Azzaz, Aleppo province.

Beirut - The Syrian army launched a threatened counter-offensive against rebel fighters in Aleppo on Saturday pouring troops into the southwest of the commercial hub, a human rights group said.

The reinforcements, which have been massing over the past few days, “have moved on the Salaheddin district, where the largest number of rebel fighters are based,” the Syrian Observatory for Human Rights said.

“The fiercest clashes of the uprising are taking place in several neighbourhoods of the city,” the head of the Britain-based watchdog, Rami Abdel Rahman, told AFP.

“You can say that the fightback has begun.” - Sapa-AFP