A high-level Lebanese security official told French news agency AFP on Wednesday that Israel fired guided missiles from a warplane to kill Hamas number two Saleh al-Arouri in a Beirut suburb.
Lebanese authorities and Hamas accused Israel of killing al-Arouri in Beirut's southern suburbs on Tuesday, with Lebanese state media saying he died with six others in a drone strike.
"Arouri was killed in strikes using guided missiles which were launched by an Israeli warplane," the official said, requesting anonymity because of security concerns.
"A drone could not have carried out such a precise strike," said the official with knowledge of the official Lebanese investigation into al-Arouri's killing.
According to the official, the guided missiles used in the attack weigh around 100 kilos (220 pounds), making them too heavy to have been fired by a drone.
Six missiles were used in Tuesday's attack, four of which exploded, the official said.
Two of the missiles that detonated pierced through two floors and exploded in a room where Arouri was holding a meeting with other Hamas officials, the source added.
A preliminary investigation by the Lebanese army indicates that remnants of that missile match those used by Israeli forces during cross-border exchanges with Hezbollah and other pro-Iran groups in southern Lebanon, the source said.
Al-Arouri is the most high-profile figure to be killed since Israel's war in Gaza broke out on October 7.
He was killed in the southern suburbs of Beirut, a Hezbollah stronghold, and it was the first strike to reach the Lebanese capital since then.
Israeli army spokesman Daniel Hagari did not directly comment on al-Arouri's killing but said his forces were "highly prepared for any scenario" in its aftermath.
In a statement Tuesday, Hezbollah warned that al-Arouri's killing in a Beirut suburb they control "will not go unanswered or unpunished".
The near-daily cross-border fire between Hezbollah and Israel has left more than 165 people dead in Lebanon, including three journalists, according to an AFP tally.
On the Israeli side, at least four civilians and nine soldiers have been killed, according to figures from the military.