The operation could begin "immediately," according to a senior U.S. official.
Israel is firing strikes into Lebanon as the conflict in the Middle East intensifies.
Israel believes it has eliminated around 30 top Hezbollah leaders over the last several weeks, including Hezbollah leader Hassan Nasrallah, who was killed in an Israeli airstrike in Beirut on Friday, U.S. and Israeli officials said.
An overnight precision strike on an apartment building in the Cola neighborhood was the first such strike in central Beirut for 18 years.
Four people were killed, including three members of the Popular Front for the Liberation of Palestine militant group.
Israel did not immediately claim the strike but is widely assumed to have carried it out.
-ABC News' Joe Simonetti
Naim Qassem, Hezbollah's deputy secretary general, addressed followers Monday in the first leadership statement since Hassan Nasrallah was killed in an Israeli airstrike in Beirut on Friday.
"The mujahadeen will continue," Qassem said of the militant group's fighters, their work informed by "what [Nasrallah] designed."
Qassem did not announce a replacement for Nasrallah, but said Hezbollah's next leader will be chosen "sooner rather than later."
Details of Nasrallah's funeral are still unconfirmed. A three-day mourning period in Lebanon began on Monday.
-ABC News' Ghazi Balkiz and Joe Simonetti
The Israel Defense Forces said it carried out an operation against more Hezbollah targets early Monday morning local time.
The Israeli Air Force attacked targets in the Bekaa region of Lebanon, the IDF said in a statement.
Targets included launchers and buildings where the IDF said weapons were held.
The Israeli Air Force also attacked what it said were military buildings in southern Lebanon.
-ABC News Will Gretsky
The death toll in Lebanon as a result of Israeli airstrikes Sunday rose to 105, according to the Lebanese Ministry of Health.
Nearly 360 individuals were wounded in the strikes, the ministry reported.
The strikes occurred in southern Lebanon, the Bekaa, Baalbek-Hermel and the southern suburbs of Beirut (Dahieh), according to the ministry.
