The U.S. State Department has ordered the departure of some embassy employees and families in Beirut "due to the volatile and unpredictable security situation."

"U.S. Embassy Beirut personnel are restricted from personal travel without advance permission. Additional travel restrictions may be imposed on U.S. personnel under Chief of Mission security responsibility, with little to no notice due to increased security issues or threats," according to the State Department advisory.

U.S. citizens in Lebanon are also being told to leave the country and the travel advisory for Lebanon remains at "do not travel."

"Due to the increased volatility following airstrikes within Beirut and the volatile and unpredictable security situation throughout Lebanon, the U.S. Embassy urges U.S. citizens to depart Lebanon while commercial options still remain available. At this time, commercial flights are available, but at reduced capacity. If the security situation worsens, commercial options to depart may become unavailable," the advisory said.

"If you choose to remain in Lebanon, be prepared to shelter in place should the situation deteriorate further. The U.S. Embassy strongly encourages U.S. citizens in Southern Lebanon, near the borders with Syria, and/or in refugee settlements to depart those areas immediately," the advisory said.

Hezbollah's command and control is in complete disarray after the killing of their Hezbollah leader Hassan Nasrallah in an Israeli airstrike on Friday, according to a senior U.S. official.

The U.S. and Israel believe they have eliminated around 30 Hezbollah leaders over the last several weeks weakening the group, the official said. There is deep skepticism and worry among the remaining Hezbollah leaders that there are spies in their ranks, according to the official.

The group's means of communication has also been dramatically disrupted after Israel blew up pagers and walkie-talkies that Hezbollah had used to communicate.

-ABC News' Martha Raddatz

Israel is preparing for a limited ground incursion into Lebanon, even after it killed around 30 top leaders within Hezbollah in recent weeks.

Israel has rejected a cease-fire proposal -- even a limited one -- in Lebanon, now bombing sites where there are suspected longer range missiles, according to a senior U.S. official. Israel is not listening to the Biden administration despite its repeated calls for a diplomatic solution.

Hezbollah leader Hassan Nasrallah was killed in an Israeli strike on a residential building in Beirut on Friday.

-ABC News' Martha Raddatz

The bomb used by Israel in Beirut on Friday very likely came from the U.S. as part of a larger military assistance program that’s been in place for decades.

The IDF described the bomb as a "bunker buster," a reference to the BLU-109 which was designed and manufactured to penetrate hardened underground bunkers.

The U.S. has used these massive 2,000-pound bombs before, typically in remote areas of countries like Afghanistan as a way to destroy enemy tunnels and underground command centers.

Use of the bunker-buster bombs in urban areas dramatically increases the risk of civilian casualties because it can turn entire neighborhoods into craters.

In May, President Joe Biden withheld a single shipment of 1,800 of these weapons to Israel out of concern Israel would use the bombs in Rafah, a highly populated area in Gaza where civilians were sheltering.

Officials say those bombs remain on hold, although Israel would likely have enough in stock for that single shipment not to make a significant tactical difference in its ongoing operations in Gaza and Lebanon.

-ABC News' Anne Flaherty