The Israel Defense Forces issued an evacuation warning for residents in the entire eastern Lebanese city of Baalbeck and the surrounding areas and key routes into the Bekaa Valley. This includes the ancient Roman temple complex, which is a UNESCO World Heritage Site.

The deliberate targeting of a World Heritage Site is a war crime under international law.

Residents have been told to evacuate their homes "immediately" and move outside the city and villages, according to the evacuation warning.

There are nearly 80,000 residents in the city, adding to the hundreds of thousands of people in Lebanon who are already displaced.

An airstrike on a residential building that killed at least 110 people in Beit Lahia in north Gaza on Tuesday -- per figures from the Hamas-run Gaza Ministry of Health -- was targeting a person acting suspiciously on its roof, an Israeli military official told ABC News.

The official said they did not know there were so many people in the building, as everyone in the area had already been told to leave.

The official added they were skeptical of the death toll provided by the Gaza Ministry of Health, a sentiment expressed by the Israel Defense Forces in a public statement regarding the incident.

State Department spokesperson Matthew Miller on Tuesday described the strike as a "horrifying incident with a horrifying result."

Emergency responders said the airstrike hit a five-story building housing displaced people, with at least 25 children among the dead. Many more people are still missing, officials said.

-ABC News' Britt Clennett

Juliette Touma, UNRWA's chief spokesperson, told ABC News the agency is "impossible to replace, especially in a place like Gaza," following the Israeli parliament's decision to ban the organization from operating in Israel.

UNRWA has warned that the move could severely curtail the aid agency's ability to get desperately needed aid into Gaza. Israeli allies abroad -- including in the U.S. -- have also warned that the Israeli parliament's move could exacerbate humanitarian concerns across Palestinian areas in Jerusalem and the West Bank.

"We have the logisticians, the humanitarian experts who know how to deliver humanitarian assistance and how to drive around and reach people in need. These are humanitarian experts who have been doing this for aid for many, many years," Touma said.

Israel has alleged that UNRWA -- which since 1950 has been responsible for supporting Palestinian refugees displaced during Israel's independence war -- is compromised by Palestinian militant groups.

A source from the Israeli Prime Minister's Office told ABC News, "UNRWA is tainted with terror and perpetuates the Palestinian problem. That is why the ban is due."

Touma disputed the assertion. "It is not as if we are the darlings of Hamas," she said. "We have continued to have a very, very bad relationship with Hamas. On a number of occasions throughout the war we have called out publicly against Hamas."

Touma said Israel is under legal obligation "to provide for the services and welfare for the community it's occupying."

Israeli authorities say they will do so without UNRWA help. But Touma said she was skeptical.

"I'm not entirely sure that they know what they're doing, practically speaking, in terms of the ability to cater and to provide humanitarian assistance to 2 million people in Gaza," she said.

The ban on UNRWA, Touma added, will not address the need for an agency serving its role.

"UNRWA exists because of the failure of the international community to reach a solution to the Israeli-Palestinian conflict," she said.

-ABC News' Britt Clennett and Guy Davies

The United Nations Special Coordinator for the Middle East Peace Process Tor Wennesland called the Israeli airstrike in Beit Lahia in northern Gaza "another appalling incident" in a "deadly series of recent mass casualty incidents," in a statement released by the U.N. Secretary-General spokesperson's office Tuesday.

"I unequivocally condemn the widespread killing and injury of civilians in Gaza, and the endless displacement of the population in Gaza," Wennesland said in the statement. "I call on all parties to abide by their obligations under international humanitarian law."