Fighting erupted in Homs on Friday, a day after townspeople said militiamen killed 14 members of a family in one of Syria's worst sectarian attacks since a revolt against President Bashar Al Assad flared in March.
The UN Security Council was to meet later in the day to discuss Syria before a possible vote next week on a new Western-Arab draft resolution aimed at halting months of bloodshed.
Russia, which joined China in vetoing a previous Western draft resolution in October and which has since promoted its own draft, said the Western-Arab version was unacceptable.
The draft contains "no fundamental consideration for our position" and is missing "key aspects that are fundamental to us," Itar-Tass news agency quoted Russian Deputy Foreign Minister Gennady Gatilov as saying.
The text, obtained by Reuters, calls for a "political transition", but not for UN sanctions against Assad's government, which Moscow opposes.
Arab monitors headed for the Damascus suburb of Douma, where government troops battled rebel fighters the previous day.
Opposition activists said Syrian security forces killed seven people overnight, including four in Homs. Two people were killed in Idlib and one in the Damascus suburb of Saqba.
Residents and activists said "shabbiha" militiamen had shot or hacked to death 14 members of the Bahader family in Homs's Karm Al Zaitoun district, including eight children, aged eight months to nine years old.
They said the slayings followed a hail of mortar rounds on the area which killed 16 people. "We also have 70 wounded," said a doctor treating casualties from the bombardment.
YouTube video footage taken by activists, which could not be independently verified, showed the bodies of five children, three women and a man in a house.
The British-based opposition Syrian Observatory for Human Rights said security forces had killed a total of 43 civilians on Thursday, including 33 in Homs, of whom nine were children.
Hamza, an activist in Homs, said the militiamen were taking revenge for deaths inflicted on their ranks by army defectors loosely grouped in the rebel Free Syrian Army.
Tit-for-tat sectarian killings began in Homs four months ago.
At the UN Security Council meeting, Morocco was expected to distribute the new draft resolution backing an Arab League call for Assad to step down. An interim unity government would then prepare for elections and enact security reforms.
Syria, which says it is pursuing its own political reforms, has rejected the Arab plan as interference in its affairs.
The 10-month-old revolt against Assad edged closer to Damascus on Thursday as troops battled rebels in a town just north of the capital and a provincial governor spoke of negotiating local ceasefires.