More than 100 people including women and children were killed by forces loyal to Syrian President Bashar al-Assad on Tuesday in Homs, the Syrian Observatory for Human Rights said on Thursday.
The Britain-based group said some of the 106 victims were burned in their homes and others were either shot or stabbed when pro-Assad forces stormed Basatin al-Hasawiya, a impoverished district of the central Syrian city.
Reuters cannot independently confirm reports due to reporting restrictions in Syria.
"The Observatory has the names of 14 members of one family, including three children, and information on other families who were completely killed, including one of 32 people," Rami Abdelrahman, head of the Observatory, told Reuters.
"This needs to be investigated by the United Nations," said Abdelrahman, who reports on atrocities committed by both sides of the 22-month-old conflict.
Syria's conflict began as a peaceful protest movement in March 2011 and has since become a full-scale civil war that has claimed more than 60,000 lives.