A senior Hamas member has been killed in a suburb of the Syrian capital Damascus, a member of the group told AFP on Thursday, accusing Israel's spy agency of being behind the attack.
Israel's defence minister responded coyly to the suggestion, telling army radio: "I'm not sure that that's necessarily right."
Hamas said the member, Kamal Hussein Ghannaja, was killed on Wednesday.
"A group of people entered his home in Qudsaya ... where he was liquidated," the official told AFP on condition of anonymity.
"According to our information, Mossad was behind the assassination," he added, referring to Israel's foreign intelligence agency.
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.
But in Israel, Defence Minister Ehud Barak said it was not "necessarily true" that Mossad was behind Ghannaja's assassination, adding that nonetheless he would not mourn the Hamas member because he was not "one of the righteous of his generation."
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.
The situation in neighbouring Syria has been a key concern for Israel, and topped the agenda of talks between Israeli officials and Russian President Vladimir Putin who visited the Jewish state earlier this week.
Barak on Thursday expressed hope that no new arms would be sent to Syria, adding that Putin "listened perfectly to what we said" on the issue, particularly on the delivery of S-300 surface-to-air missiles.
Israel is still technically at war with Syria, but the armistice line separating the neighbours has been largely quiet in recent years, leading some to suggest that the fall of President Bashar al-Assad could be bad for the Jewish state.
However in recent months, after initially declining to make public comment, Israeli leaders have condemned Assad's crackdown, saying it is only a matter of time before he is ousted.
"The Assad family is losing control over Syria," Barak said on Thursday.
"Assad will fall, the forces of the opposition control significant parts of Syria. But the longer it takes, the more difficult it will be to stabilise the situation."