Islamist extremists forced to abandon their base in Syria's central Hama province left behind a mass grave with a dozen corpses, mostly civilians, including four women, local activists reported Monday.
The discovery at Kafr Zeta was likely to fuel the drive to force foreign fighters from the Islamist State of Iraq and Syria out of the conflict and, most probably, Syria.
On the fifth day of a surprise offensive against ISIS by a wide range of Syrian insurgents, fierce fighting was reported in Raqqa, a provincial capital that is an ISIS stronghold, and in at least two districts of Aleppo, Syria's biggest city.
ISIS reportedly had abandoned Jarabulus, a major border crossing with Turkey, and its forces were under siege at Tal Abyad, another border point.
The offensive appears to have galvanized many of Syria's disparate fighting forces into a level of cooperation rarely seen on the ground, and it may have given new life to remnants of the U.S.-backed Free Syrian Army, which many wrote off as a spent force a month ago.
Dan Layman, a spokesman for the Syrian Support Group, a Washington-based group that raises money for the rebels, said that rebels formerly identified with the FSA were now fighting in one of two groups, the Syrian Revolutionary Front, with 10,000 to 15,000 fighters, and the Jaysh al Mujahideen, or Mujahideen Army, which has about 12,000 fighters.
A third rebel faction, the Islamic Front, which supports the establishment of a Syria governed by Islamic law, has taken a leading role in the fighting and was believed to be in control of Jarabulus and pressing for control of Tal Abyad.
The Nusra Front, yet another rebel faction, also has taken a role in the fighting against ISIS. Like ISIS, Nusra is an al Qaida affiliate and traces its roots also to al Qaida in Iraq. The U.S. government a year ago designated Nusra a terrorist group, saying it was simply another name for al Qaida in Iraq, which renamed itself ISIS in April. The two groups frequently cooperated with one another in battles against Syrian government forces.
Nusra reportedly collaborated with the other rebel factions to arrange ISIS' departure from its Kafr Zeta base.
According to Muhannad Jnaid, a rebel captain, ISIS initially had agreed last week to surrender the Kafr Zeta base in a deal brokered by Nusra. But a group of ISIS fighters who had sneaked away from the main group opened fire on the rebels, killing five.
Fighting resumed until Sunday, when the ISIS forces again sent a message through Nusra that they were ready to surrender the base and their weapons, Jnaid told McClatchy. On Sunday night, the ISIS forces departed in the company of Nusra troops; other rebel units occupying the base discovered, however, that not all the ISIS units had left their weapons behind.
"We've asked Nusra to bring the rest of the weapons back," he said.
The rebels found the mass grave when they searched the base. There were at least a dozen corpses, with many residents of other towns. Ahmad Bayoush, an activist, said three of the dead were from his hometown of Kafr Anbil, and the corpses of all three showed signs of torture. He identified one as Mansour Assalloum, a 16-year-old boy; the other two were men.
Activist Basil Darwish said four women were among those buried in the grave, two from the city of Hama and two from the nearby town of Latamneh. He identified one of the victims as Abdulkarim al Qasim, a lawyer from the nearby town of Morek.
Hannah Allam in Washington contributed to this report.
By Roy Gutman
McClatchy Foreign Staff