Israel-Gaza-Lebanon updates: Iranian president responds to Israel's retaliatory attacks

The Israel Defense Forces claimed late Hezbollah leader Hassan Nasrallah's gold-filled bunker is located underneath a Beirut hospital, which hospital officials said was being evacuated Monday out of an abundance of caution.

"There are millions of dollars in gold and cash in Hassan Nasrallah's bunker. Where is the bunker located? Directly under Al-Sahel Hospital -- in the heart of Beirut," IDF spokesperson Rear Adm. Daniel Hagari said in a video address Monday.

The IDF released 3D renderings of the hospital building and the bunker it said belonged to Nasrallah, who was killed in Israeli airstrikes in Beirut last month, but has not provided tangible proof. Hagari said the Israeli air force is monitoring the site but added, "We will not strike the hospital itself."

"We are not at war with the people of Lebanon. We are at war with Hezbollah," he said.

Following Hagari's remarks, Lebanese hospital officials said the hospital is being evacuated out of an abundance of caution for the safety of the patients. Lebanese Parliament member Fadi Alameh, the owner of the hospital, said he has requested that the Lebanese army and United Nations Interim Force in Lebanon investigate the Israeli allegations.

Lebanese official Wiam Wahhab said the "talk of weapons depots" at the hospital "is illogical and false."

"This points to the beginning of targeting hospitals, and the army must deploy around the hospital and protect it," he said.

Dr. Youssef Bakhash, the president of the Lebanese Order of Physicians, told the Lebanese media group Al Jadeed that the "pretext of the existence of tunnels and funds beneath Sahel Hospital is aimed at targeting and disrupting the healthcare sector."

Israel’s planned attack on Iran will mark the "beginning of a war" that will last "many months," retired Israel Defense Forces Brig. Gen. Amir Avivi told ABC News.

Israel's war with Hezbollah had gone incredibly well and the IDF had surpassed its own expectations in degrading the Iranian proxy, Avivi said, adding that the same mentality would be applied to dealing with the Iranian regime itself.

"We have a historical opportunity to deal with Iran so they don’t pose another threat to Israel," said Avivi, the founder of the right-wing think tank Israel's Defense and Security Forum.

Israel's retaliatory strike on Iran will be "fierce and strong and very surprising" when it happens, he said.

-ABC News' Tom Soufi Burridge and Jordana Miller

The Israel Defense Forces said it hit 300 Hezbollah targets in southern Lebanon in the past 24 hours, which saw an intense night of airstrikes on Beirut.

Seven brigade commanders, 21 battalion commanders and 24 company commanders for Hezbollah were killed in its ongoing operations, the IDF said.

More strikes against Hezbollah targets are expected all over southern Lebanon Monday night, IDF spokesperson Rear Adm. Daniel Hagari said.

There's no indication yet whether classified documents on Israel's retaliation plans were leaked or hacked, White House national security spokesperson John Kirby told reporters Monday.

"I'm just not able to answer your question whether it was a leak or a hack at this point. We'll let the investigation pursue its logical course there," Kirby said.

Kirby said that President Joe Biden was "deeply concerned" about the incident, and that while they don't expect more documents to be revealed, they are on high alert amid the investigation.

"We're certainly going to keep our antenna up and our eyes open for any potential future disclosures," he said.

-ABC News' Cheyenne Haslett