Militiamen loyal to President Bashar al-Assad shot dead at least 20 civilians when they stormed the homes of three unarmed families on the edges of opposition districts in the city of Homs on Wednesday, the Syrian Observatory for Human Rights said.
The shabbiha (Assad's militiamen) broke into three houses overnight and slaughtered a family of five - the father, wife and their three children, a family of seven in another house and eight in a third, dissident-in-exile Rami Abdelrahman, who heads the British-based Observatory, told Reuters.
There was no comment from Syrian authorities and the report could not be verified because the authorities have placed tight restrictions on access to the country.
Abdelrahman said the attacks occurred near al-Fardaos roundabout and near al-Naziheen and Karm al-Zeitoun districts, where loyalist forces have been advancing after heavy bombardment of the city of one million, 140 kms (88 miles) north of the capital, Damascus.
He gave the names of the families as Ghantawi, Tirkawi and al-Zamel.
The shabbiha (ghosts in Arabic) are acting as if they are at the peak of their power and that they can do anything to prevent the Assad regime from falling, Abdelrahman said.
He would not be drawn on the religion of either the attackers or the victims in the mixed city where sectarian killings have been reported and staunch Sunni Muslim districts have been main target of a large-scale armoured offensive by Assad's forces that began on Monday.
On January 27, Alawite shabbiha militiamen killed 14 members of a Sunni family in Homs in one of the grisliest sectarian attacks in the eleven-month uprising raging in the Alawite-dominated country, according to activists and residents said.
Eight children, aged eight months to nine years old were among 14 Bahader family members shot or hacked to death in a building in the mixed Karm al-Zeitoun, they said.
Members of the Alawite sect have been killed also by Sunnis opposed to Assad who have taken up arms in the city, and abductions of Sunni Muslims and Alawites have been reported also in the last four months.
The shabbiha trace their origin to a group of Assad's relatives in the coastal city of Latakia, who controlled businesses and touted AK-47 automatic rifles from black Mercedes S series limousines, nicknamed 'shabah' (the ghost).
Their numbers have grown since a popular uprising against 42 years of Assad family rule erupted in March, drawing in other members of Assad's minority Alawite community, which has dominated the majority Sunni country for five decades.
The shabbiha are overwhelmingly Alawites in Homs and in the city of Hama further north, but large numbers of Sunnis have been recruited into their ranks in cities such as Aleppo and Damascus, according to opposition sources.
(Reporting by Khaled Yacoub Oweis, Amman newsroom; Editing by Louise Ireland)