A high-level Lebanese security official told AFP on Wednesday that Israel fired guided missiles from a warplane to kill Hamas number two Saleh al-Aruri in a Beirut suburb.
Lebanese authorities and Hamas accused Israel of killing Aruri in Beirut's southern suburbs on Tuesday, with Lebanese state media saying he died with six others in a drone strike.
"Aruri 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 Aruri'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 Aruri was holding a meeting with other Hamas officials, the source added.
A preliminary investigation by the Lebanese army indicates that remnants of those missile match those used by the Israeli army during cross-border exchanges with Hezbollah and other pro-Iran groups in southern Lebanon, the source said.
Aruri is the most high-profile figure to be killed since the Hamas-Israel 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 Aruri's killing but said the military was "highly prepared for any scenario" in its aftermath.
In a statement Tuesday, Hezbollah warned that Aruri'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, most of them Hezbollah members but also more than 20 civilians 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.