At least 50 soldiers of the Syrian Army’s 17th division were killed and a number of them were beheaded Friday during an ambush by fighters of the Islamic State of Iraq and Syria. The attack was mounted on an army base outside the northern Syrian city of Raqqa, which is controlled by ISIS.

“At least 50 soldiers were ambushed, some of them were killed in fighting, but most of them were beheaded,” said Rami Abdel Rahman, the director of the Britain-based Syrian Observatory for Human Rights quoted in an Agence France-Presse report. During the same offensive, 74 people were killed in the last 24 hours, the human-rights group said.

“Allah be praised, 75 soldiers of the 17th division were captured at Abu Shared and they were beheaded,” an ISIS sympathizer reportedly tweeted.

A Twitter account reportedly connected with ISIS published pictures of beheaded corpses and the heads of five soldiers killed in the attack, claiming they belonged to the 17th division. A video posted online with the title in German, “What is left of Division 17 in Raqqa,” shows ISIS fighters rummaging through the living quarters of 17th division troops and destroying pro-Assad flags and posters while expressing disgust at the presence of alcohol and cigarettes found there, reports said.

Raqqa, the capital of a Syrian province, has completely fallen outside the control of the Syrian regime headed by President Bashar Assad. The 17th division is one of three Syrian army divisions still holding positions in the ISIS-controlled region, and it has a large base there. The army repositioned the 17th division Friday, reports said.