The British-based Syrian Observatory for Human Rights said women and children were among the 106 people killed by forces loyal to President Bashar al-Assad forces who stormed Basatin al-Hasawiya, a poor district on the edge of Homs, on Tuesday.
The massacre in the central city came the same day twin explosions killed over 80 people at Aleppo's university in the north, according to the group.
Reuters cannot independently confirm reports due to reporting restrictions in Syria.
Syrian warplanes and troops pursued a countrywide offensive on Thursday, activists and state media said, bombing rebel-held areas and clashing with insurgents who have pushed into cities.
Government forces clashed on Thursday with insurgents in the cities of Deraa, Hama, Homs, Aleppo, Damascus and east of Deir al-Zor, the Observatory said. Only the coastal Assad strongholds of Latakia and Tartous were spared violence.
Opposition activists said 15 people, including 7 children, were killed when an air strike hit a family home in Husseiniyeh, a suburb on the outskirts of the capital.
They sent Reuters footage of people dragging the limp bodies of children out of the rubble.
In Hama province, the government said it had secured some areas and displaced families were returning to the area of Zor Abi Zaid after armed forces "cleansed the area completely of terrorists", a term authorities use for the rebels.
Activists and Turkish news agencies reported renewed clashes on the Syrian border town of Ras al-Ain, where rebel forces have been fighting armed Kurdish groups for control.
The local Turkish Dogan news agency said one man on the Turkish side of the border was wounded by a stray bullet overnight and that schools in the area had been closed due to the clashes on the Syrian side.
In the power vacuum, some Kurdish groups are trying to assert control over parts of Syria through fights with rebels and government forces. The Observatory said clashes broke out between Kurdish militants and the Syrian army in Rameilan, a town in the northeast.
FAMILY OF 17 REPORTED KILLED
Activists said 17 members of the Khazam family had been killed during Tuesday's raid on Basatin al-Hasawiya.
"This needs to be investigated by the United Nations," said Abdelrahman, a Syrian who has documented human rights violations in Syria since 2006 and now reports on killings by both sides.
The United Nations says 60,000 have been killed in the 22-month-old conflict. Several massacres have been reported, most blamed on pro-Assad forces but some also on rebel fighters.
The town of Houla in Homs province was the scene in May 2011 of the killings of 108 people, including nine children and 34 women, which U.N. monitors blamed on the army and pro-Assad militia.
The United Nations sent observers to Syria in April 2011 but after several attacks on their convoys they left in August, complaining both sides had chosen the path of war.
Abu Yazen, an opposition activist in Homs, said the rebel Free Syrian Army occasionally entered the farmland of Basatin al-Hasawiya to attack a nearby military academy.
"Assad's forces punish civilians for allowing the rebels to enter the area," he said. Other activists said the raid was carried out by pro-Assad militia.
The government and opposition blame each other for two explosions at Aleppo's university on Tuesday which killed at least 87 people, many of them students attending exams, in the deadliest attack on civilians to hit the commercial hub since rebels laid siege to it over the summer.
U.S. ambassador to the United Nations Susan Rice said the attack was "beyond horrific".
"According to eyewitnesses, regime jets launched the strikes," she said on her Twitter account.
Russia, which has backed Assad throughout the revolt both in rhetoric and through its veto of U.N. Security Council resolutions condemning Assad, dismissed suggestions Damascus was behind the explosions.
"I cannot imagine any bigger blasphemy," Russian Foreign Minister Sergei Lavrov told journalists during a visit to Tajikistan.
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