The military commander of the Green Battalion, an Al-Qaeda affiliated brigade, was killed in Qalamoun battles near Damascus, sources reported.
Abu Muhjin al-Omani, originally from Oman, was killed during the storming of the Bassel Hospital in Deir Attiyeh.
Rebels on Friday seized a key town in Qalamoun province, which had been under army control since the outbreak of the conflict, an opposition monitoring group and the official opposition said, according to AFP.
The Green Battalion appears to be yet another Islamic group in Syria that has pledged allegiance to Al-Qaeda and its leader Ayman al-Zawahiri.
Zaman al-Wasl could not independently confirm the account.
The majority Christian town north of Damascus is home to 10,000 people and is situated on the strategic route linking the capital to Homs in central Syria.
It was seized by the jihadist Islamic State of Iraq and Greater Syria and the Nusra Front, as well as other Islamist fighters, said the Observatory, which relies on a network of activists, doctors and lawyers on the ground for its reports.
Translated and edited by The Syrian Observer