BEIRUT: Hezbollah party leader Samir Kuntar was killed in an Israeli airstrike in Damascus early Sunday, the Lebanese group and Syrian government sources said.
Israel welcomed his death, but stopped short of confirming responsibility for the strike that killed him.
Hezbollah, a Shiite Muslim group, said Kuntar was "martyred" in an Israeli raid on the residential district of Jaramana in the Syrian capital, but gave no details.
Israel released Kuntar, a Druze, in 2008 as part of a prisoner swap with Iranian-backed Hezbollah and he is since believed to have joined the group, which has sent hundreds of its members to fight alongside forces loyal to Syrian President Bashar Assad.
On his release, Kuntar was welcomed as a hero in Beirut.
Hezbollah's official media said Kuntar would be buried Monday in a Shiite cemetery in its main stronghold of Dahiya in the southern suburbs of Beirut. The party, which mourned him, also opened a condolences hall to receive the public.
Syrian Information Minister Omran al Zubi said the authorities were investigating the attack but pointed the finger towards Israel, though he also fell short of blaming it.
"The party that gains most from the assassination of Kuntar is the Zionist enemy whom we have long known for these cowardly attacks," Zubi told Hezbollah's Manar television station.
Official Syrian media said an Israeli aerial strike hit a six-story residential building in the Jaramana district.
"I am not confirming or denying anything to do with this matter," Israeli Housing and Construction Minister Yoav Gallant told Israel Radio.
Kuntar spent 29 years in an Israeli prison over his alleged role in 1979 killings. He was released along with four other Lebanese prisoners in a 2008 swap deal with Hezbollah in exchange for the bodies of two Israeli soldiers killed during the 2006 war.
After his release, Kuntar kept a low public profile and it was not immediately clear what role Kuntar, born in 1962, played in the fighting in Syria.
Israel has carried out multiple strikes in Syria targeting Hezbollah and Syrian army positions over the last two years. Most of the strikes have hit what were reported to be weapons convoys destined for Hezbollah in Lebanon.
Syrian state media said Kuntar was involved in a major offensive launched earlier this year by the Syrian army and its allies near the Syrian Golan Heights in Quneitra near the Israeli border against the opposition fighting to topple Assad.
Rebels in southern Syria also said Kuntar was present in battles this year to defend a Syrian air base near the Druze majority city of Sweida close to the border with Jordan that rebels sought to capture.
Israeli Justice Minister Ayelet Shaked accused Kuntar of overseeing covert Hezbollah entrenchment on the Syrian Golan Heights, a strategic plateau overlooking northeastern Israel.
Yaakov Amidror, Israel's former national security adviser, predicted Hezbollah would seek to exact "small revenge" for Kuntar's killing.
"It would not be in their interest, and if they did so, they would have a big problem," Amidror said, alluding to Israel's threats to respond to any major Hezbollah attack with strikes in Lebanon.
Syrian government loyalists said the explosions that killed Kuntar were an Israeli strike.
The National Defence Forces in Jaramana, part of a nationwide grouping of loyalist Syrian militias under the umbrella of the army, mourned Kuntar on its Facebook page.
"Two Israeli warplanes carried out the raid which targeted the building in Jaramana and struck the designated place with four long-range missiles," the NDF in Jaramana Facebook page said. Jaramana is a bastion of government support and is the home of many of Syria's Druze minority as well as Christians.
Sunday's attack was Israel's first on a Hezbollah target since January when it hit a convoy in the Golan Heights area of Qunaitra, killing six Hezbollah members and an Iranian commander.
Hezbollah retaliated days after the strike by targeting an Israeli military convoy in the occupied Shebaa Farms, killing two Israeli soldiers.
At the time, Hezbollah chief Sayyed Hasan Nasrallah vowed to respond to any Israeli attack on the party's members in Syria.