Rebels have 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.
Several thousand rebel fighters have gone on the offensive in Aleppo.
Shells crashed down at a steady rate and clashes were widespread, leaving layers of dust and smoke over Aleppo, according to the residents of the northern city and the Syrian Observatory for Human Rights on Friday.
"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 in 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 30-year-old resident of the central district of Sulimaniyeh who only identified himself as Ziad.
"Everyone is terrified. I have never heard anything like this before."
The outgunned rebels, a rag-tag army made up of mutinous soldiers and civilians who have taken up arms in the 18-month battle to oust President Bashar al-Assad's regime, declared an all-out assault for Aleppo on Thursday.
After his remarks an AFP correspondent counted about 16 mortars fired from 5pm to 7.30pm there, with a shot about every 15 minutes in three army-held areas, including Sulimaniyeh and Sayyid Ali.
A resident says one of the mortars hit a residential building and killed four people from the same family, including an old man and a young child.
In Damascus, Presidents Assad's forces launched assaults on several rebel areas in the north of the capital on Friday, said the Observatory.
"Regime forces stormed the neighbourhoods of Barzeh, Jubar and Qaboon in Damascus, cutting off streets and breaking into and raiding houses. They arrested a large number of residents," it said.
More than 30,000 people have been killed overall in violence since the March 2011 outbreak of the revolt against the president, according to the Britain-based Observatory.
