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 Beirut's southern suburbs, in one of the most powerful raids since Israel intensified its campaign of bombardment last week.
AFP footage showed giant balls of flame and thick smoke rising from the site that was attacked.
Israel's military said it had hit "targets belonging to Hezbollah's intelligence headquarters in Beirut".
The attack came a week after the Israeli military said it killed Hezbollah leader Hassan Nasrallah in air strikes on the group's headquarters in south Beirut.
Israel has intensified its aggression on Lebanon dramatically since September 23, targeting the country's southern villages, and Beirut's southern suburbs, among other areas.
Nearly 2,000 have been killed in the country since Israel began its cross-border conflict with Hezbollah almost a year ago, after Israel began waging its brutal military operation in the Palestinian Gaza Strip on October 7.