Israel-Gaza updates: IDF says it exposed Hamas tunnel under Shifa Hospital

Fighting between Hezbollah and Israeli forces intensified Sunday in southern Lebanon, where the terrorist group has claimed responsibility for launching a series of missile strikes on northern Israel, Israeli military officials say.

“Hezbollah is dragging Lebanon into a war that may happen, and it is making mistakes," Israeli Defense Minister Yoav Gallant said on Saturday. “If it makes mistakes of this kind, the ones who will pay the price are first of all the citizens of Lebanon. What we are doing in Gaza we know how to do in Beirut."

Hezbollah has claimed responsibility for at least five attacks in northern Israel, including one it says resulted in numerous deaths and injuries. The terrorist group also claimed one of its missile strikes targeted Israel's Zarit Barracks on the Israeli-Lebanese border.

Hezbollah has been designated a terrorist organization by multiple countries, including the U.S. and Israel.

Fighting between Hezbollah and Israeli troops intensified Saturday night into Sunday. Local news media broadcast images of the heavy clashes in the hills along the border and smoke rising.

Lebanese Prime Minister Najib Mikati released a statement saying his country does not want war but has made a contingency plan in case it is drawn into the conflict between Israel and Hamas.

"What matters to me is that Lebanon stays away from war and looks forward to stability," Mikati told the Al Jazeera network.

During the Al Jazeera interview, Mikati called for an immediate ceasefire in Gaza.

-ABC News' Marcus Moore

At least nine Americans remain unaccounted for and U.S. officials believe they are being held hostage by Hamas in Gaza, White House national security adviser Jake Sullivan told ABC News Sunday.

"There are ongoing negotiations involving the Israelis, the Qataris, and we, the United States, are actively engaged in this as well, because we want to make sure that we bring home those Americans who have been taken hostage as well as all of the other hostages," Jake Sullivan told ABC "This Week" co-anchor Jonathan Karl.

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US is ‘actively engaged’ in ongoing hostage negotiations: Jake Sullivan

ABC News’ Jonathan Karl interviews National Security Adviser Jake Sullivan on “This Week.”

Pressed by Karl on the total number of hostages, Sullivan said America doesn't have a "precise number."

"We know the number of missing, and that's the number the Israelis have given. But we don't know how many of those are still alive," Sullivan said. "As far as the Americans are concerned, there are nine missing American citizens, as well as a missing legal permanent representative, a green card holder."

Sullivan said he plans to meet with family members of the American hostages this week.

-ABC News' Fritz Farrow