The Israel Defense Forces claims to have killed at least 50 Hezbollah members, including six senior commanders, in "significant airstrikes" on Monday.

The IDF said it conducted a series of strikes on underground Hezbollah command centers in southern Lebanon.

Hezbollah has not commented on the IDF's strikes.

Israeli officials claimed Tuesday that their forces have killed the replacement for Hezbollah leader Hassan Nasrallah.

"We damaged Hezbollah's capabilities. We have eliminated thousands of terrorists, including Nasrallah himself, Nasrallah's successor, and the successor of Nasrallah's successor," Israeli Prime Minister Benjamin Netanyahu said in a video address on Tuesday. "Today, Hezbollah is weaker than it has been in many years."

Israeli Minister of Defense Yoav Gallant also said during a situation assessment on Tuesday that Nasrallah's replacement was "probably also eliminated."

"Hezbollah is an organization without a head," Gallant said. "There is no one to make decisions, no one to act."

Hashem Safieddine, a top Hezbollah official, was widely believed to succeed Nasrallah after the leader was killed in an Israeli airstrike last month.

Hezbollah has not commented yet on Israel's claims. Deputy Secretary-General Naim Kassem said earlier Tuesday that Hezbollah's "resources and capabilities remain in good shape."

"Our resistance on the front is cohesive and the administration is cohesive," he said in a video address delivered from an unknown location.

Hanan Balkhi, the regional director of the World Health Organization Eastern Mediterranean Regional Office, said Tuesday that 77 health workers have been killed and 74 others wounded by Israeli attacks since the beginning of October.

Health infrastructure has been "severely damaged," the WHO wrote on X, with the organization verifying 36 attacks on health facilities so far in October.

Hezbollah Deputy Secretary-General Naim Kassem said Tuesday that the Iran-backed group will not be cowed by Israel's ongoing air and ground campaign in Lebanon.

"The longer the war goes on, the deeper Israel will find itself in trouble," Kassem said in a video address delivered from an unknown location. Prime Minister Benjamin Netanyahu "can say that he wants war, but he cannot achieve his goals from it," he added.

More Israelis in the north of the country will be displaced as Hezbollah expands its operations, he said.

Hezbollah will continue cross-border attacks and "expanding the range of the missiles," the leader said.

"This war has not affected our will and will not affect our determination to confront," Kassem said. "Our resistance on the front is cohesive and the administration is cohesive."

"Our resources and capabilities remain in good shape," Kassem said, despite weeks of intense Israeli airstrikes across Lebanon. "Our command and control is solid. Look at how our operations have increased in the last few days." Still, Kassem also said Hezbollah supports Lebanese government efforts to secure a cease-fire.

Kassem said the U.S. bears responsibility for the ongoing war. "Israel and America and the West are trying to put more pressure on us to make us afraid," he continued.

"Without American support, the Israeli aggression would have stopped within a month," Kassem said.

-ABC News' Joe Simonetti and Somayeh Malekian