BEIRUT (AP) - An international human rights group on Friday accused Syrian government forces and pro-regime militias of carrying out summary executions earlier this year that left at least 248 people dead in two predominantly Sunni Muslim towns along the Mediterranean coast. The allegations by Human Rights Watch came as intense negotiations by top American and Russian diplomats were underway in Geneva over securing President Bashar Assad's chemical arsenal implicated in the alleged chemical attack near Damascus last month that killed hundreds. It was the Aug. 21 attack in the sprawling Damascus suburb of Ghouta that prompted the U.S. to threaten Assad's forces with a military strike. Washington and its allies said Syrian government troops fired warheads that contained a nerve agent into the suburb, most likely sarin. The U.S. says more than 1,000 people were killed in the attack; other estimates put the death toll at 500, at the least. More than 100,000 people have been killed so far in Syria's civil war. The New York-based group said in its new report, released Friday, that mass killings took place in the towns of Bayda and Banias on May 2 and 3. It said the report was based on accounts of people and witnesses who saw or heard government and pro-government forces detain and then kill their relatives. The group's activists interviewed 15 Bayda residents and five from Banias, as well as survivors and local activists to compile a list of names of 167 people killed in Bayda and 81 in Banias. The two towns are predominantly populated by Sunni Muslims, who dominate the armed revolt against Assad's regime. They are located in Syria's coastal area, the heartland of the ruling Alawite sect, an offshoot of Shiite Islam and a group that the president also belongs to. "While the world's attention is on ensuring that Syria's government can no longer use chemical weapons against its population, we shouldn't forget that Syrian government forces have used conventional means to slaughter civilians," said Joe Stork, the acting Middle East director at HRW. Survivors told us devastating stories of how their unarmed relatives were mowed down in front of them by government and pro-government forces. In the 68-page report released Friday, HRW says it has witness accounts and video evidence to support claims that the "overwhelming majority" of the victims in the two towns were killed after military clashes ended and opposition fighters had retreated from the area. The actual number of casualties is likely to be higher as it's difficult to access the area, Banias in particular, to account for the dead, the group said. At the time, the Syrian government acknowledged its troops had been operating in Bayda and Banias but said they had battled and killed many "terrorists," the government's term for rebels fighting to topple Assad's regime. Syria's crisis stared in March 2011 as largely peaceful protests against Assad's rule. The uprising turned into civil war after some opposition supporters took up arms to fight a harsh government crackdown on dissent. In the past two years, the fighting has taken increasingly sectarian overtones. In the aftermath of the alleged chemical attack, Assad denied responsibility and accused U.S. officials of spreading lies without providing evidence. In an interview Thursday, the Syrian president described the Aug. 21 attack as a "U.S.-organized provocation." Speaking to Russia's state Rossiya 24 news channel, Assad agreed to a Russian plan to secure and destroy his chemical weapons but said the proposal would work only if the U.S. halts threats of military action. Russian President Vladimir Putin hailed Syria's move, telling an international security gathering on Friday in Kyrgyzstan that joining the Chemical Weapons Convention has proven Damascus' good faith. It shows that Syria has "serious intentions to embark on that path," Putin said at the summit dominated by Russia, China and Iran, all Assad allies. On Monday, Russia proposed that Syria avoid a U.S. military strike by surrendering control over its chemical weapons to the international community for eventual dismantling. Damascus quickly jumped at the offer and top U.S. and Russian diplomats opened talks in Geneva on Thursday to discuss the specifics. U.S. Secretary of State John Kerry and a team of U.S. experts were to meet their Russian counterparts Friday for the second day of talks on a plan how some 1,000 tons of chemical weapons stocks and precursor materials as well as potential delivery systems could be safely inventoried and isolated under international control. Russia, backed by China, has repeatedly used veto power at the Security Council to block resolutions calling for sanctions against Assad's regime.