Both groups said at least 50 people were killed. The Observatory, which has a network of activists around the country, said the dead included 13 children. It added that about 100 people were wounded.
An amateur video posted online by activists showed more than a dozen bodies lined up inside a room. They included about 10 children who were covered with sheets that only showed their bloodied faces.
"Houla was subjected to a massacre," a man could be heard saying inside the room.
The Observatory said in one incident in Houla, a family of six were killed when their home received a direct hit.
Homs has been among the hardest-hit provinces in the government crackdown.
Attacks like Friday's, as well as strikes by rebel forces on government troops, have persisted despite the deployment of more than 250 U.N. observers who have fanned out across Syria to monitor a cease-fire brokered by international envoy Kofi Annan.
Despite the daily violations, U.N. Secretary-General Ban Ki-moon said Thursday that there was no "plan B" for the Annan initiative.
The northern city of Aleppo, a major economic hub, has remained largely supportive of Assad throughout the uprising but anti-regime sentiment has been on the rise in recent weeks.
On Friday, Syrian forces fired tear gas and live ammunition to disperse thousands of protesters in Aleppo calling for Assad's ouster, killing five people, activists said.
Also Friday, a group of Lebanese Shiites who were kidnapped in Syria were released in good health, three days after gunmen abducted the men as they returned from a religious pilgrimage.
The kidnappings fueled fears that Lebanon was getting drawn into the bloody conflict in neighboring Syria. In the hours after Tuesday's abductions, protests erupted in Beirut's Shiite-dominated southern suburbs, where residents burned tires and blocked roads.