The official said Ghannaja was one of the deputies of Mahmud al-Mabhuh, a senior Hamas military commander found dead in a Dubai hotel room in 2010. Investigators in the Gulf emirate have accused Mossad of that murder.

Syria has long allowed Hamas to operate offices in Damascus, but in recent months, the Palestinian group has quietly moved most of its operations elsewhere as an uprising that is spiralling into civil war has rocked the country.

Local Coordination Committees, made up of anti-regime activists on the ground in Syria, accused the regime of President Bashar al-Assad and his militiamen, known as shabiha, of being behind Ghannaja's assassination, claiming that he was "tortured to death".

"He was visiting Syria and nobody knew he was in the country apart from the security services who gave him permission to enter," said Hifawi Mohamed, a member of the LCC in the Palestinian refugee camp of Yarmuk in Damascus.

"The way the body was mutilated and the attempt to burn the house are all methods that point to the involvement of the security forces" Mr Mohamed told AFP.