BEIRUT — Syrian activists and rebel fighters said Monday at least 100 people and possibly more than 400 were killed in a five-day Syrian government offensive on a predominantly Sunni area of the Damascus countryside. The death toll could be the largest from a single military campaign in nearly a year.
Activists described a bloody war zone inside Jdeidet al-Fadel, an area west of the Syrian capital that remained critically isolated on Monday, a day after government forces had reportedly withdrawn to the town’s outskirts, trapping the surviving residents inside and keeping medical workers and activists out.
‘‘The regime does not allow anyone to get in or out of the area. There is no way to save the injured people,’’ said a rebel military spokesman who uses the pseudonym Musab Abu Qatada.
The Syrian Observatory for Human Rights, a Britain-based watchdog group, said Monday that activists had documented 101 dead inside Jdeidet al-Fadel, including at least 10 women and three children. But the Observatory said the toll could exceed 250 because there were many people who could not be located while the regime forces were deployed in town.
The Local Coordination Committees, another activist group, put the death toll at 483, the Associated Press reported. It was impossible to verify the number of casualties or missing beyond activist accounts.
Activists also said a number of the area’s residents were arrested during the weekend as rebel fighters ran out of ammunition and retreated from the area, allowing forces loyal to President Bashar al-Assad to accelerate their offensive.
They described the looting of area shops and burning of homes.
‘‘Those arrests were taking place in a street where the [rebel Free Syrian Army] was not present, and they could not stop it,’’ said Aya Mahaini, an activist who spoke by Skype, using an alias, from the neighboring suburb of Madhamiyat al-Sham. The suburb also has been shelled repeatedly in recent days. The sounds of nearby explosions repeatedly interrupted the call.
The United Nations says at least 70,000 people have been killed, and nearly a quarter of Syria’s population has been displaced, in more than two years of brutal civil war.
The Syrian Arab News Agency, a mouthpiece for the Assad government, said Monday that government forces had ‘‘inflicted heavy losses upon terrorists in the town of Jdeidet al-Fadel in Damascus Countryside, injuring a number of them [and] killing others.’’
Assad’s government refers to those fighting to end his rule as ‘‘terrorists.’’
A pro-regime Facebook page called ‘‘Syria 24’’ reported Monday that government forces in Jdeidet al-Fadel had killed ‘‘600 terrorists’’ from Jabhat al-Nusra, a rebel jihadist group that the US government has labeled a terrorist organization.
Videos posted online Sunday and Monday purported to show rows of bodies from the beleaguered town. Some appeared to have been shot in the face. In one video, a camera moved slowly over what looked like 10 bodies covered by blankets and body bags, as another person revealed their faces. At least two appeared to be children.
Syrian activists and rebels said the killings in Jdeidet al-Fadel appear to be the largest massacre since a government assault last summer on the nearby Damascus suburb of Darayya, which by activist accounts left at least 300 people dead.
The Local Coordination Committee for Jdeidet Artuz, the broader area that encompasses Jdeidet al-Fadel, posted to its Facebook the names, ages, and causes of death of more than 100 people.
Among them were Hanan Aslan, 6, who was killed by a mortar shell; Khaled Ibrahim Salloum, 33, felled by a sniper shot; and Akram Moussa, age unknown, who the site said was dismembered using machetes. Many other causes of death were listed as burning; the victims were adults, their identities unknown. Other entries said the victims were ‘‘executed at the hands of the regime in the field.’’
Activists said the Jdeidet al-Fadel area of the Damascus countryside is one of a few contested suburbs at risk of falling under rebel control, as the nation’s multitude of rebel forces have advanced toward the capital in recent months.
The region currently provides the Syrian government with a critical lifeline to the Lebanese border.
‘‘The [rebel] battalions are trying to connect the liberated areas, to surround the regime and strangle it,’’ said Abu Qatada, a spokesman for the Damascus Military Council, which is part of the Free Syrian Army.
On Monday, Abu Qatada said the area was back under total regime control.
Activists said Jdeidet al-Fadel is populated predominantly by Sunni refugees from the Golan Heights, Syrian territory that was seized by Israel in the 1967 regional war, as well as those recently displaced by fighting near Damascus.
The area had no Internet access and only a marginal presence of rebel fighters when the government forces pushed in, activists said Monday. The flow of information out of the area therefore has been limited.