The Local Coordination Committees said 44 people were killed in what the group described as a massacre, the BBC reported. The killings happened in the Jobar district of Homs. Twenty people were from a single family and 16 were from another.
Government forces have retaken Homs after weeks of bombings and attacks.
The BBC said activists groups report the execution of men from Hom's devastated Baba Amr neighborhood, the slaying of entire families and the mass rape of women.
More than 7,500 people have died as a result of the violence in Syria over the past 12 months, U.N. officials said.
Kofi Annan, the Joint Special Envoy of the United Nations and the League of Arab States for Syria, Thursday called for an immediate end to the killings and warned against the use of force to bring an end to the crisis.
"I hope no one is thinking very seriously of using force in the situation. I believe any further militarization will make the situation worse," Kofi Annan said at a joint press conference in Cairo with the Secretary-General of the Arab League, Nabil El-Araby.
"We have to be careful that we don't introduce a medicine that is worse than the disease," he said. "And we do not have to go very far in the region to find an example of what I am talking about."
Annan was in Cairo for discussions with the Arab League ahead of his scheduled visit this weekend to Syria.
The former U.N. Secretary-General has been tasked with helping to end the deadly violence gripping the country and find a peaceful political solution.
"The level of violence is excessive and unacceptable by any standards," Annan said. "This cannot continue. The violence and the killing must stop and stop immediately. There is an urgent need to change course."
Syria's deputy oil minister has allegedly resigned and joined opposition efforts to force President Bashar Assad from power, French media reported.
France 24 said Abdo Hussam el Din told the news channel he no longer wished to work for "a criminal regime."
A man identifying himself as the deputy oil minister posted a video on YouTube Wednesday saying he was defecting.
"I am joining the revolution of this noble people who will not accept injustice," the man said in Arabic. "I've been part of this government for 33 years, and I have acquired many titles, and I do not want to retire serving the crimes of this regime."
Heavy fighting was reported Thursday near the Syrian-Turkish border, activists said.
At least 40 people were killed Wednesday, including seven children, a woman and two military recruits, activists said. The LCC said 26 people were killed in Homs, seven in Idlib, two in the Aleppo suburb of Atareb, three in Daraa and two in Damascus suburbs.
Syrian state media said 14 "army and law enforcement martyrs" were buried Wednesday.
In Washington, the Obama administration said for the first time it was ready to provide direct assistance to Syria's rebels.
U.S. Defense Secretary Leon Panetta told the Senate Armed Services Committee Wednesday the administration was preparing to supply communications and other "non-lethal" equipment to Syrian opposition forces, although he said the opposition's lack of cohesion and structure posed a challenge.
Meanwhile, the top U.N. relief official said through a spokeswoman the shattered Baba Amr neighborhood of the Syrian city of Homs she visited Wednesday was "devastated" and all-but-devoid of inhabitants.
"She says that the parts [of Homs] they saw were completely devastated," Amanda Pitt, spokesman for Valerie Amos, the U.N. undersecretary-general for humanitarian affairs and emergency relief, was quoted by the British newspaper the Daily Telegraph as saying.
"She said Homs feels like a city that has been completely closed down," Pitt said.
The 45-minute visit to the former opposition stronghold was the first inspection of Homs by an independent outside observer since Syrian armed forces besieged it more than a month ago to crush a key hub of armed resistance.
Her visit, under Syrian Red Crescent escort, also marked the first time the relief agency was allowed to enter the district since the siege ended March 1.
The Assad regime first promised to let humanitarian relief into the area last Friday, but troops loyal to the regime continually told aid workers the neighborhood was sealed, citing security problems.