ALEPPO: Rebels unleashed an unprecedented barrage of mortar fire against troops in Aleppo after announcing a “decisive”battle for Syria's second city, residents and a watchdog say.

Shells crashed down at a steady rate and clashes were widespread, leaving layers of dust and smoke over Aleppo, according to the residents and the Syrian Observatory for Human Rights.

“The fighting is unprecedented and has not stopped since Thursday. The clashes used to be limited to one or two blocks of a district, but now the fighting is on several fronts,” the Observatory's Rami Abdel Rahman told AFP.

Residents of neighbourhoods previously spared the worst of the two-month-old battle for Aleppo also told AFP the violence was “unprecedented”.

“The sound from the fighting... has been non-stop,” said a resident of the central district of Sulimaniyeh, who identified himself only as Ziad. “Everyone is terrified. I have never heard anything like this before.”

Rebels claimed they had advanced on several fronts, particularly in the southwest, but admitted they had failed to make any significant breakthrough.

“On the Salaheddin front, we took one of the regular army bases,” said Abu Furat, one of the leaders of the Al-Tawhid Brigade, the most important in the city.

But he admitted that the fighters had to retreat from Salaheddin because they were outgunned. “To win a guerrilla street war, you have to have bombs and we don't,” he said.

Abu Furat said that 25 soldiers were killed in the assault, while another rebel fighter said 20 of his comrades died on the battlefield and 60 were wounded.

The Observatory which gave initial estimates of 60 people killed across the country on Friday, half of them civilians, said at least five civilians and five rebels died in Aleppo.

“We heard soldiers on their radio calling their chiefs to ask for reinforcements. They were crying and saying 'we are all going to die,'” a rebel said.

By Friday afternoon the intensity of the fighting abated, as rebels appeared to focus their attention on other objectives, such as Omayyad Mosque in the centre of the Old City, an AFP correspondent said.

The Observatory's Abdel Rahman said the fighting was not yielding major gains for either side: “Neither the regime nor the rebels are able to gain a decisive advantage.”

Protesters brave fighting

The outgunned rebels, a rag-tag army made up of mutinous soldiers and civilians who have taken up arms to oust President Bashar al-Assad's regime, declared an all-out assault for Aleppo on Thursday.

Afterwards, an AFP correspondent said mortars were fired about every 15 minutes into army-held areas, including Sulimaniyeh and Sayyid Ali.

“One mortar round hit a residential building and killed four people from the same family, including an old man and a young child. We tried to carry them away to bring them to the hospital but they were already dead,” one resident said.

Violence also raged in Damascus where troops attacked several rebel areas in both the north and the south of the capital, leaving three civilians dead, the Observatory said.

Despite the violence, thousands of protesters took to the streets of Aleppo and other cities in support of the unification of the Free Syrian Army as factionalisation appears to undermine the anti-regime revolt.

The Observatory said demonstrations were held after the main weekly Muslim prayers in the Fardus and Sukari neighbourhoods of Aleppo, as well as in the central province of Homs, Hama further north and Idlib in the northwest.

“May God protect the Free Syrian Army,” demonstrators chanted in Kfar Zita in Hama province.

The conflict has dominated proceedings at the UN General Assembly in New York, where UN and Arab leaders expressed concerns the country could become a “regional battleground.”

UN Secretary General Ban Ki-moon, Arab League leader Nabil al-Arabi and special envoy Lakhdar Brahimi shared those fears as they met at UN headquarters to discuss “the appalling levels of violence,” a UN spokesman said.

US Secretary of State Hillary Clinton, meanwhile, prepared to host a meeting of the “Friends of Syria” group at which Syrian activists will urge world leaders to do more to help people caught up in the conflict.

And Sergei Lavrov, the foreign minister of Russia, which has repeatedly blocked UN Security Council action against its longstanding Syrian ally, was to address the General Assembly.