Syrian state media accused insurgents on Saturday of killing 123 people, the majority of them civilians, during a rebel offensive this week to take the northern town of Khan al-Assad.
A two-year revolt-turned-civil war has left more than 100,000 people dead and both forces loyal to President Bashar al-Assad and rebels are accused by rights groups of war crimes.
State news agency SANA said that "armed terrorist groups" committed a "massacre ... mutilating the bodies of the martyrs and throwing them in a big hole on the outskirts of the town, in addition to incinerating a number of [their] bodies."
The accusations come a day after a rebel group, calling itself the Supporters of the Islamic Caliphate, posted a video on YouTube of around 30 bodies of young men piled up against a wall who they said were pro-Assad militiamen.
The Syrian Observatory for Human Rights, an anti-Assad monitoring group, cited activists on Friday in Khan al-Assal who said that more than 150 soldiers were killed on Monday and Tuesday in and around the town, including 51 soldiers and officers who were executed.
Having won Western support in the early stages of the revolt, the opposition has since succumbed to infighting between moderate and hardline Islamist groups. Meanwhile, Assad has been able to rely on Iran, Russia and Lebanon's militant Hezbollah group to support his crackdown.
Islamist militants fought with ethnically Kurdish units on Saturday near the border with Turkey in part of an ongoing territorial dispute.
An official in Turkey said there were reports that the al-Qaeda linked Nusra Front had approached the border and that shelling from Syria had fallen on Turkey. It was not clear who controlled the nearby border gate of Ras al-Ain, he said.
The war — pitting Sunni majority rebels against Assad's own Alawite sect and Shi'ite Hezbollah — has descended into sectarian hatred.
The army continues to hit major cities with artillery and airstrikes. The Observatory reported on Saturday that 29 civilians, including 19 children and four women died when a surface-to-surface missile hit a building in the northern city of Aleppo, once Syria's commercial hub.
Insurgents have focused on taking isolated army outposts, mostly in rural areas while forces loyal to Assad have made gains in recent months around the capital Damascus and the central city of Homs.