Human Rights Watch accused the Syrian government-linked forces of executing at least 248 people
, including women and children, following clashes with opposition fighters in two towns earlier this year.
Human Rights Watch says the killings in the coastal towns of al-Bayda and Baniyas were among the "deadliest instances of mass summary executions" during Syria's two and a half year-long civil war.
The group's report says the executions followed clashes between government and rebel forces on May 2-3. After opposition fighters retreated, the report said Assad fighters entered homes, rounded up men from each neighborhood, and shot them execution style.
HRW documented at least 23 women and 14 children, including infants, it says were killed by government forces in al-Bayda. It said in both towns, government or pro-government forces executed, or tried to execute, entire families.
Syria's government has admitted to killing "terrorists," its name for rebels, and possibly committing what it called "mistakes" during the military operation in the two towns. But HRW says the "overwhelming majority" were executed after the clashes had ended.
The report comes amid a flurry of diplomatic activity and possible U.S. military strikes meant to punish the Syrian government for what Washington believes was a chemical weapons attack carried out by the Assad government last month that killed hundreds in a rebel-held town near Damascus.
Joe Stork, Human Rights Watch's acting Middle East director, says the executions show that the world "shouldn't forget that Syrian government forces have used conventional means to slaughter civilians."
Several recent videos have also emerged that appear to show Syrian rebel forces committing executions of government troops and loyalists. In one of the most gruesome videos, a rebel commander is seen ripping the heart out of a government soldier's chest and eating it.
HRW said in its report that the U.N. Security Council should "ensure accountability for these crimes by referring the situation to the International Criminal Court."