Syrian rebels along with other jihadist militant groups launched a major offensive on government held areas of southwestern Aleppo on Sunday to break the siege on the city, rebels and monitor groups said.

Forces loyal to President Bashar al-Assad have surrounded rebel held districts in Aleppo and tightened their siege, since 17 July. The Syrian regime has also cut off the Castello road, the main supply route, which leads out of Aleppo and the north towards Turkey.

Jihadist groups, including the newly formed Jabhat Fatah al-Sham (former Al-Qaeda affiliate known as Jabhat al-Nusra/Nusra Front) and the influential Ahrar al-Sham on Sunday said that they had taken over positions in the government held areas of southwestern Aleppo in the first few hours after launching the offensive to try and reopen a new supply route.

The Syrian army has confirmed on state run TV that the rebels had indeed launched an offensive but said that the army pushed the militants back from an air force artillery base and opposed the claim that insurgents seized the Hikma school.

Jabhat Fatah al-Sham launched two car bombs in suburban Rashidin against Syrian regime positions, as the battle raged until evening, Syrian Observatory for Human Rights said. The monitor group added that this attack was by far the biggest campaign waged against government forces by the insurgents, since fighting escalated in recent months.

"It will be a long and difficult battle."The [Syrian] army is supported by a large number of Iranians and fighters from Hezbollah, not to mention the Russian planes," the Observatory head Rami Abdel Rahman was quoted as saying to AFP.

At least 11 people were killed in the rebel rocket attacks, including three children, which was aimed at the government held district of Hamadaniyeh in Western Aleppo, the monitor said. Other attacks occurred in southern parts of the city towards regime held area of Ramussa, it added.

Aleppo, which was Syria's biggest city once, is now divided into government controlled west and rebel controlled east since mid 2012. However, on 28 July, Thursday, Syrian government along with its Russian allies, announced the opening of three humanitarian corridors to allow civilians and unarmed rebels to flee the besieged areas of Aleppo. According to Russian government, only 169 people had been able to leave by 30 July, Saturday. Around 300,000 people still reside in the besieged parts of Aleppo.

Syrian rebels
Syrian rebels walk in a damaged factory in the al-Khalidiya neighbourhood of Aleppo [File Picture]Reuters