Syrian rebels including jihadists have counter-attacked the army and its allies in a bid to break a siege on eastern Aleppo, insurgents say.

The assault on Friday, employing heavy shelling and suicide car bombs, was mainly focused on the city's western edge by rebels based in the countryside outside Aleppo.

It included Jabhat Fateh al-Sham, a former affiliate of al-Qaeda previously known as the Nusra Front, and groups fighting under the Free Syrian Army (FSA) banner.

The Syrian Observatory for Human Rights, a British-based war monitor, said more than 15 civilians had been killed and 100 wounded by rebel shelling of government-held western Aleppo. State media reported that five civilians were killed.

There were conflicting accounts of advances in areas on the city's outskirts.

Aleppo, Syria's biggest pre-war city, has become the main theatre of conflict between President Bashar al-Assad, backed by Iran, Russia and Shi'ite militias, and Sunni rebels including some supported by Turkey, Gulf monarchies and the United States.

The city has been divided for years between the government-held western sector and rebel-held east, which the army and its allies put under siege this summer and where they launched a new offensive in September that medics say has killed hundreds.

Fateh al-Sham said in a statement that rebels had gained control over Dahiyet al-Assad, a suburb with a low-rise residential district of about a square kilometre on the southwest corner of the city.

Syrian military source said earlier that the army and its allies had thwarted what he called "an extensive attack" on south and west Aleppo. A state television station reported that the army had destroyed four car bombs.

Abu Anas al-Shami, a member of the Fateh al-Sham media office, told Reuters from Syria the group had carried out two "martyrdom operations", after which its fighters had gone in and had been able to "liberate a number of important areas". A third such attack had been carried out by another Islamist group.

The powerful role played by Jabhat Fateh al-Sham, listed by many countries as a terrorist group, has complicated Western policy towards supporting the anti- Assad opposition.

The United States has prevented more powerful weapons such as anti-aircraft missiles from being supplied to rebels partly out of fear they could end up in jihadist hands.

The Syrian military source said Friday's attack had been launched in coordination with Islamic State, a group against which all the other rebels, including Fateh al-Sham, have fought.

Islamic State fighters did clash with the Syrian army on Friday at a government- held airbase 37km east of Aleppo, next to territory the jihadist group already controls, the Observatory reported.