Hizbollah has warned that it will "punish" Israel for the killing of a senior commander.
Hassan Lakkis was shot near his home on the outskirts of Beirut on 3 December.
"All evidence indicates that Israel is behind the assassination," Hassan Nasrallah said on television on Friday.
"The killers will be punished sooner or later," said Mr Nasrallah. "Those who killed our brothers will not know safety anywhere in the world."
Israel, which fought a war lasting 34 days with Hizbollah in 2006, denies the accusation.
The BBC reports little is known publicly about Lakkis, but he was reputedly an expert in weapons manufacture. He is said to have trained in warfare in Iran.
Lakkis was shot and killed outside his home in Hadath, south-east of Beirut at around midnight on 3 December. Two men were reportedly seen running away afterwards.
''These automatic accusations are an innate reflex with Hizbollah," Israeli foreign ministry spokesman Yigal Palmor said at the time.
"They don't need evidence, they don't need facts. They just blame anything on Israel."