Fighters from the Islamic State have killed more than 150 captured soldiers in northern Syria in the past two days, a monitoring group said Thursday. Video images posted online appeared to show the men being marched through the desert in their underwear by the extremists and then lying dead in the sand.
The mass killing marked a dark end to the battle for control of the Tabqa air base in Raqqa province. The insurgents seized the base Sunday after the deadliest fighting so far between the Islamic State and government forces.
The killings were reported on the same day that Syrian rebel fighters captured 43 U.N. peacekeepers near the demarcation line between Syria and the Israeli-occupied Golan Heights, after heavy fighting in the area between non-Islamic State rebel fighters and government troops.
As it has stormed through northern Iraq and seized Mosul, that country’s second-largest city, Islamic State has often distributed graphic images of its dead adversaries, to enlarge its reputation and terrify its enemies. But even by the group’s usual brutal standards, the video of jihadist fighters taunting humiliated, nearly naked men as they were led to their death were horrifying, sending shock waves through Syrian communities that have stood by President Bashar Assad through more than three years of civil war.
Compounding the reaction were apparent attempts by the government to play down the loss of the base. The state news agency, SANA, reported on the day the base fell that troops there had withdrawn and regrouped, and were fighting successfully nearby.
The next day, Walid al-Moallem, Syria’s foreign minister, made only a brief reference to the battle in an hourlong interview, conceding that the base had been lost but claiming that all troops and aircraft had been successfully withdrawn.
Anger erupted Thursday after administrators of a Facebook page dedicated to the soldiers stationed at the base posted one video of the men being marched through the desert, and another that showed their bodies — more than 120 of them — lying in a long line.
“Stop circulating false news,’’ wrote one commenter under the name Zahraa al-Hassan, referring to the government’s claims. The commenter called the Assad government “a filthy failure that has destroyed the country’s trees and people and allowed ISIS to rise,’’ using an abbreviation for another of the Islamic State’s names.
Many comments posted on the site assailed Gen. Fahd Jassem al-Freij, the defense minister, who retained his post in a new Cabinet announced Wednesday despite the loss of three important military facilities to Islamic State fighters in little more than a month.
An illustration posted on the page sarcastically addressed Assad’s press office, saying it had promised to “do everything necessary to follow up on the shortcomings that have led to the loss of a number of areas and a large number of martyrs for the homeland.’’
Many Syrians have stood by Assad through the conflict because they see him as a symbol of the state or they fear that the rebels who are trying to topple him will destroy the country. Many members of Syria’s Alawite minority believe their survival depends on Assad because the extremist elements of the rebellion consider Alawites to be infidels and hold the entire group responsible for Assad’s actions.
Still, worry has grown among government supporters as the war has dragged on and as Islamic State has gained strength and territory with little interference from the Syrian army.
The brutal coda to the battle for the Tabqa air base was likely to raise further complaints about Assad’s prosecution of the war.
The Syrian government did not comment on the killing of its captured soldiers.
Videos posted online by Islamic State supporters gave glimpses of the soldiers’ final hours. In one, men who appear to be the prisoners are seen running in a long line through a stretch of desert as bearded Islamic State fighters laugh and herd them like sheep.
“The state of Islam!’’ the fighters yell, a common Islamic State slogan, and the soldiers reply, “It remains.’’
Another video shows scores of captives lying on the concrete floor of a large room while one is questioned by Islamic State fighters who are off camera.
“How many people have you killed?’’ the fighters ask. “How many have you raped?’’ The captive soldier shakes his head and says, “No one.’’
When he tells the interrogators that he is an Alawite, they insult him and say, “We’ll return you to hell, God willing.’’
A Lebanese Islamic State fighter who was reached through the Internet and gave his name only as Yousef said that the soldiers seen dead in the video were part of a military column that came to the area in an attempt to rescue troops who had fled the air base.
“We ambushed them and arrested them,’’ he said.
Yousef said the Islamic State fighters made the soldiers run in the desert to tire them out, and then locked them in a room where they were beaten.
“Then we took them out and shot them,’’ he said.
The Syrian Observatory for Human Rights, an opposition group that tracks casualties in Syria, said that more than 150 captured soldiers had been killed by Islamic State since Wednesday. But the group’s director, Rami Abdulrahman, raised doubts about the Islamic State account. Abdulrahman said the military column sent to the area of the base had evacuated 60 soldiers, and that he had seen no proof that the men in the videos were the slain soldiers.
In southern Syria, rebels and government forces have been clashing fiercely in the area near the demarcation line that is monitored by U.N. peacekeepers, especially around Quneitra, the only border crossing between Syria and the Israeli-held territory. On Wednesday, fighters from a number of Syrian rebel groups, including the Nusra Front, which is affiliated with al-Qaida, wrested control of the crossing from Syrian government forces. Islamic State fighters were not reported to be involved.
The 43 peacekeepers seized in that area Thursday were Fijians. The United Nations said in a statement that it was making every effort to secure their release. A number of Filipino peacekeepers from the same U.N. mission were held by rebels last year and later released unharmed.
A spokesman for U.N. Secretary-General Ban Ki-moon condemned the detention of the peacekeepers and demanded their immediate release.
Anti-government activists in the area who work with the rebels were not immediately available for comment.
The Syrian Foreign Ministry issued a brief statement saying the government “holds the terrorist groups and the sides backing them fully responsible for the safety of the kidnapped soldiers and demands their immediate release.’’
Fighting continued in the border region Thursday, as the Syrian government mounted airstrikes. It did not comment on the fighting or say whether any of its soldiers had been killed.
Besides Fijians and Filipinos, the U.N. force in the Golan Heights includes personnel from India, Ireland, Nepal and the Netherlands. The force has been monitoring a cease-fire and military disengagement agreement between Israel and Syria in the area since 1974.