A high-level Hezbollah source said on Saturday that contact with Hashem Safieddine, widely touted as potentially the group's next leader, had been lost following Israeli strikes this week.
"Contact with Sayyed Safieddine has been lost since the violent strikes on Beirut's southern suburbs" early on Friday, the official told AFP.
"We don't know if he was at the targeted site, or who may have been there with him," he added.
A second source close to Hezbollah also confirmed that communication had been cut off with Safieddine and that his whereabouts were unknown.
Hezbollah "is trying to reach the underground headquarters that were targeted, but every single time Israel starts striking again to impede rescue efforts," he said.
Safieddine "was with Hezbollah's head of intelligence," known as Hajj Murtada, when the strikes took place, he said.
Both sources requested anonymity to discuss sensitive matters.
Early on Friday, a source close to Hezbollah said Israel had conducted 11 consecutive strikes on the group's south Beirut stronghold, in one of the most powerful raids since Israel intensified its campaign of bombardment campaign last week.