Key Lebanese militant Samir Qantar has been killed in a rocket strike near the Syrian capital, Damascus, Hezbollah has said.
The Lebanese Shia militant group blamed Israel for the air strike.
Qantar was jailed in Israel in 1979 for a notorious deadly attack, and freed as part of a controversial prisoner swap with Hezbollah in 2008.
An Israeli minister welcomed his death but did not confirm that Israel was responsible.
When asked about Israeli involvement, Construction and Housing Minister Yoav Gallant told Israel Radio: "I am not confirming or denying anything to do with this matter."
But he added: "It is good that people like Samir Qantar will not be part of our world."
Later on Sunday, at least two rockets were fired into northern Israel from Lebanon, Lebanese security forces told AFP news agency.
The Israel Defense Forces (IDF) said three rockets struck open areas, with no reports yet of damage or injuries.
Qantar was known as the "dean of Lebanese prisoners" for the time he spent imprisoned in Israel.
He was convicted of murder over an attack on a civilian apartment block in Nahariya in 1979, carried out when he was 16.
Two policemen, a man and his four-year-old daughter were killed. A baby girl was accidentally smothered by her mother as she hid in a cupboard.
He was accused of killing the four-year-old girl with a rifle butt, which he denied.
His release in 2008 in exchange for the bodies of two Israeli soldiers captured by Hezbollah in 2006 was highly controversial.
Qantar is believed to have become a key figure in Hezbollah since his release.
Hezbollah has sent hundreds of fighters to fight alongside troops loyal to Syrian President Bashar al-Assad in the country's conflict.
In September, the US state department designated him a terrorist saying he had become one of Hezbollah's "most visible and popular spokesmen".
"Since Qantar's return, he has also played an operational role, with the assistance of Iran and Syria, in building up Hezbollah's terrorist infrastructure in the Golan Heights," it said.
The rockets hit a residential building in Jaramana near Damascus on Saturday night. The area is a stronghold of government supporters.
The Assad loyalist group, the National Defence Forces in Jaramana, said: "Two Israeli warplanes carried out the raid which targeted the building in Jaramana and struck the designated place with four long-range missiles."
Israel is believed to have carried out a number of attacks inside Syria during its civil conflict, targeting Hezbollah.