The Syrian army has pressed its assault on rebels in commercial capital Aleppo, while both sides reported atrocities and Arab foreign ministers postponed a planned meeting on the 17-month conflict.
The exiled opposition said pro-government militia had executed 10 civilians in a roundup in the flashpoint central city of Homs, while the official SANA news agency reported the murder of one of its staff, in the latest case of a pro-government journalist being killed.
The Arab League gave no reason for the indefinite postponement of its planned meeting in Saudi Arabia that had been due to discuss a replacement for international envoy Kofi Annan who announced his resignation earlier this month.
On Tuesday, Saudi Arabia is to host an Islamic summit focused on Syria to drum up support for the anti-regime revolt. Arab foreign ministers of the Gulf held talks late Sunday in the Saudi city of Jeddah to prepare for the summit.
In Aleppo, troops shelled rebel-held districts as fighting flared anew around a southwestern neighbourhood that rebel fighters had quit last week, the Syrian Observatory for Human Rights said.
The Shaar, Tariq al-Bab, Sakhur, Hanano and Bustan al-Qasr neighbourhoods all came under bombardment, as the army pressed a ground offensive it launched on Wednesday to recapture areas seized by rebels since July 20, the group said.
The Britain-based monitoring group also said that "communications of all forms have been cut off in the city of Aleppo as well as large areas of the province since the morning".
In the city of Homs, three children on a minibus were killed as they tried to flee with their parents from the Shamas district, where a military operation took place, it said.
The Observatory said at least 29 people were killed across the country on Sunday, including 15 civilians.
In Damascus, gunfire was reported in the Qadam neighbourhood. Outside the capital, machinegun fire was heard in the town of Al-Tal, where 15 civilians were killed in shelling and clashes the previous day.
They were among 148 people - 85 civilians, 43 soldiers and 20 rebels - killed across Syria on Saturday, according to the Observatory.
On the situation in the capital, the pro-government Al-Watan newspaper spoke of "foiled bids to break the calm in Damascus, which was cleansed of terrorist groups who terrified residents".
In Aleppo, the paper said the army was poised to assault the Sukari neighbourhood in the south of the city, after its recapture of the nearby Salaheddin district on Thursday.
Activist groups said 10 civilians were executed in a roundup of military-aged men in the Shamas district of Homs.
"Militiamen detained nearly 350 people from the Shamas district, assembled them in a courtyard and executed 10 of them," activist group, the Syrian Revolution General Council, said.
"The fate of the nearly 340 others is unknown and we fear greatly that they have met the same fate as the 10 martyrs," the group added.
The official SANA news agency said the head of its home news department, Abbas Ali, was assassinated by an "armed terrorist group" at his home outside the capital on Saturday evening.
On Friday, rebels abducted three state television journalists as they accompanied government troops operating near Damascus, the Syrian Observatory said.
It came after a bomb attack on state television headquarters wounded several people last week and after an al-Qaeda-linked group claimed the abduction and murder earlier this month of state television presenter Mohammed al-Saeed.