Senior Hamas official identified as Kamal Hussein Ghannaja was gunned down in Damascus, earlier this month. Finger pointed at both Israel and the Assad regime.
Izzat Risheq, a senior Hamas leader, took to Facebook to announce the death of Kamal Hussein Ghannaja, also known as Nizar Abu Mujahed. The post said that he was killed in a night attack on 27 June in the Syrian capital.
Israeli media, which described Ghannaja as a former deputy of slain Hamas military commander Mahmud al-Mabhouh, said he was shot dead in his home.
Al-Mabhouh was killed in a Dubai hotel room in 2010. Investigators in the Gulf emirate have accused Israel's spy agency Mossad of being behind the killing, though Israel never confirmed or denied involvement.
A senior member of Hamas, speaking anonymously, told AFP Ghannaja was killed in a suburb of Damascus and accused Mossad of being behind the murder.
"A group of people entered his home in Qudsaya... where he was liquidated. According to our information, Mossad was behind the assassination," the official said.
Israel's defence minister Ehud Barak told army radio: "I'm not sure that that's necessarily right."
Hamas established headquarters in Damascus in 1999 but the relationship between Syria and the Islamist movement became strained after the anti-Assad uprising started to gain pace.
Hamas has now evacuated most of its operatives from Syria in a bid to distance itself from the Syrian government, though it has refused to publicly call for Assad to step down or cut all ties with the regime.
In a separate report, the online edition of Israel's Yedioth Ahronoth, Ynet, said an opposition figure, speaking on condition of anonymity had blamed the Syrian regime for the killing.
It said the activist, a former journalist, insisted Ghannaja was tortured before he was killed.
According to the source, the order to kill the Hamas operative was in retaliation to the group's lack of support on Assad during the conflict.