Syrian military officials said more than 80 civilians in Adra were executed by Islamic rebels and other civilians were kidnapped for use as human shields, RT reported Monday.
Government forces were conducting a large-scale operation against Jabhat al-Nusra and Liwa Al-Islam fighters, who recently captured the town. Syria's official news agency said about 1,000 militants were Adra when government-backed forces entered the town Friday.
The opposition group Local Coordination Committees said aerial attacks by Syrian government forces in Aleppo killed at least 83 people, including at least 27 children and eight women, Sunday. At least 50 people were reported injured.
The Local Coordination Committees said helicopters dropped barrel bombs on 12 neighborhoods in the city, where people strongly back forces against President Bashar Assad's government, CNN reported Monday. The opposition group said 135 people died in fighting across Syria Sunday.
Meanwhile, military sources told RT, a Russian English-language news channel, the "armed groups have performed an execution of civilians" in Adra in areas taken back by Syrian forces.
Russia has supported Assad's regime and opposed an international military intervention since the start of Syria's civil war in March 2011.
One resident told RT the Islamist rebels massacred residents when they entered Adra Wednesday.
"The situation was terrible -- with killing, atrocities, and fear as the background. Unidentified armed men came into town, but it was obvious that they were Jabhat al-Nusra militants," Muhammad Al-Said told the Russian news channel. "The worst crime they committed was that they toasted people in ovens used to bake bread when those people came to buy it. They kidnapped and beat up many."
The United Nations has estimated more than 100,000 people have died and hundreds of thousands of people have been injured since the Syrian civil war began as peaceful anti-government protests in March 2011.
More than 2.3 million people have fled Syria, and another 4.25 million Syrians have been displaced within their country since the civil war began, an Amnesty International report released Friday indicated.