Izz al-Din Shaikh Khalil, 42, who was expelled by Israel from the Gaza Strip in 1992, died after an explosion blew up his car in the early hours of Sunday in Damascus, a Hamas spokesman told Aljazeera.net
"We believe it was action taken by the Israeli security agencies," said Usama Hamdan, adding that they "talked about this just a few weeks ago".
Aljazeera's correspondent in Damascus reports that Khalil left his home at around 0800 GMT and got into his vehicle. After driving a few metres, he answered a telephone call and the car blew up.
"When Khalil left his house, he got into his car and drove for about 50 metres," said Laila Mawaid. "He then received a phone call and his car blew up, killing him. His body was torn into pieces."
Three passersby were wounded and windows of nearby high-rise buildings as well as a nearby car were damaged.
A Syrian minister said the explosion was caused by a booby-trapped car.
Later on Sunday, an Israeli cabinet minister was quoted as saying: "I don't know anything about it." But in the first official Israeli reaction to the killing, acting Public Security Minister Gideon Ezra said: "I am glad."
The Associated Press quoted security sources, speaking on condition of anonymity, as acknowledging Israel's involvement.
Earlier this month, Israeli army chief Moshe Yaalon warned that Israel would "deal with ... those who support terrorism" including those in "terror command posts in Damascus".
The assassination follows a report in Saturday's edition of the Arabic language al-Hayat newspaper that the intelligence services of an unnamed Arab country had agreed to an Israeli request to supply it with information about Hamas' overseas structure and leaders living abroad.
"I believe it is a matter of action and reaction," said Hamdan.
"They are killing our people every day. The whole world has to expect Palestinians will continue their resistance against this occupation until they free their homeland."
Khalil was one of 400 Palestinian
activists exiled by Israel in 1992
Syrian security forces are investigating the assassination, Hamdan said.
Khalil, who was born in Gaza City, was among some 400 Palestinians, mainly Hamas members, deported by Israel to Lebanon in 1992.
Some were later allowed to return home, but others such as Khalil chose to remain abroad and coordinate the movement's activities from outside.
In March 2004, Israeli assassinated Hamas' co-founder and spiritual leader Shaikh Ahmad Yasin in a missile strike as he left a mosque in Gaza City.
Yasin's successor Abd Al-Aziz al-Rantisi was killed a month later in a similar Israeli attack in Gaza City.
Hamas said it would avenge his slaying.
"These crimes which unify the Palestinian blood inside and outside Palestine will not terrorise us or stop us from pursuing the path of jihad and resistance"
"Hamas ... holds the Zionist occupation forces responsible for this crime," the group said in a statement.
"It stresses that these crimes which unify the Palestinian blood inside and outside Palestine would not terrorise us or stop us from pursuing the path of jihad and resistance."
A member of Hamas's political bureau, Muhammad Nazzal, said "the Zionist entity wants to transfer its crisis to outside Palestine".
He cautioned Israel had "failed to humiliate us [Hamas] and eliminate the resistance inside the occupied Palestinian land. You [Israel] will also fail to do so outside Palestine".