Dozens of detainees were freed from the headquarters, housed in a children’s hospital, according to the report.
“The fate of hundreds of the ISIL fighters, who were in the place, is not clear yet,” the Observatory said.
The fighting, pitting secular and moderate Islamist opponents of Syrian President Bashar al-Assad against ISIL insurgents, has continued in northern and eastern Syria for almost a week. Dozens of people have reportedly been killed.
The Syrian conflict, which has lasted for nearly three years, has resulted in several radical groups imposing strict Islamic rule in areas under their control.
The chief of Syria’s Al-Nusra Front, an Al-Qaeda affiliate, called Tuesday for an end to fighting between rebel groups and the jihadist Islamic State of Iraq and the Levant (ISIL). The message came as the Syrian Observatory for Human Rights, a monitoring group, said at least 274 people had been killed in the clashes that erupted last Friday.
In an audio recording posted on Twitter, Abu Mohamed al-Jolani announced an initiative to end the fighting, including a “ceasefire” and the establishment of an independent Islamic committee to serve as mediator.
“If the fighting is not resolved, the jihad formed by the muhajireen (foreign fighters) and the ansar (local fighters) risks losing lots of ground”
“This unfortunate situation pushed us to launch an initiative to solve the situation,” Jolani said. “It consists of forming a committee based on Islamic law and composed of the key brigades (and)… the establishment of a ceasefire,” he said.
The initiative also calls for an exchange of prisoners and urges all fighters “to give priority to the fight against the regime.”
In recent days, widespread fighting has broken out pitting coalitions of Islamist and moderate rebel forces against ISIL.