Live Updates: Israeli Strike Hits Central Gaza Hospital Complex

The Israeli military said early Monday that it had struck what it described as a Hamas command center within a former hospital, and that the armed group had used it to coordinate attacks against Israeli troops. That claim could not be independently confirmed.

The strike in Gaza followed a weekend of intense military activity along Israel’s northern border with Lebanon, home of the Iran-backed militia Hezbollah.

The Israeli military said on Sunday that a drone strike by Hezbollah on a military base in northern Israel had killed four soldiers and injured dozens of others, and that the group had fired more than 100 rockets toward Israel on Sunday alone.

And as a weekslong Israeli assault on Hezbollah in Lebanon continued, at least 51 people were killed and 174 others injured on Saturday, the Lebanese authorities said.

Here’s what else to know:

• Polio site struck: A strike overnight on a school compound in central Gaza where families were sheltering has resulted in fatalities and damage, according to UNRWA, the main U.N. agency that aids Palestinians. The head of the agency, Philippe Lazzarini, cited reports that 20 people had been killed at the facility, in the city of Nuseirat. The Israeli military did not immediately respond to a request for comment. Lazzarini said the facility was to have been used as a site for polio vaccinations, as a mass anti-polio campaign in Gaza resumed on Monday.

• U.S. pledges forces to Israel: The United States said on Sunday that it was sending an advanced missile defense system to Israel, along with around 100 American troops to operate it. That will mark the first deployment of American forces to Israel since the Hamas-led attacks there last October. The Israeli military is weighing a retaliatory attack on Iran, which launched about 200 missiles at Israel on Oct. 1.

• Israeli tanks enter U.N. peacekeeping base: Israeli tanks entered a United Nations peacekeeping base early Sunday morning, according to the U.N. The mission said the presence of Israeli forces there risked undermining the U.N.’s neutral status and made its personnel a target for Hezbollah. The Israeli military said that its forces were trying to evacuate troops who had come under Hezbollah missile fire.

• Reporting from Lebanon: Journalists from The New York Times and other news organizations entered southern Lebanon on Sunday under the supervision of the Israeli military. They visited what the military said was a secret Hezbollah outpost equipped with explosives and mines.

Southern Lebanon, along with the Bekaa Valley in the country’s east, continue to be pounded by Israeli bombardment. The Israeli military issued new evacuation warnings for more than two dozen towns and cities in southern Lebanon on Monday.

Lazzarini said the facility was to have been used on Monday as a site for polio vaccinations, as a mass anti-polio campaign in Gaza resumes. Nearly 560,000 children were vaccinated against the disease during the first round of the campaign a month ago, and aid agencies plan to administer second doses across Gaza over the next two weeks. Israel and Hamas have agreed to pause fighting for several hours a day in areas where vaccines are being administered.

“The inviolability of U.N. premises must be respected at all times,” Mr. Guterres said in a statement on social media on Sunday. “Attacks against peacekeepers are in breach of international law and may constitute a war crime.”

The Israeli military said that its soldiers had entered the peacekeeping base as they tried to flee from Hezbollah missile fire and were in contact throughout the episode with the U.N. peacekeeping mission, known as UNIFIL.

The mission came under Israeli fire several times last week, and Israeli officials have called on the United Nations to pull its peacekeeping forces back. Prime Minister Benjamin Netanyahu said on Sunday that the United Nations’ refusal to do so “makes them hostages of Hezbollah,” the armed Lebanese group that the Israeli military has been targeting in a weekslong air and ground offensive.

“This endangers both them and the lives of our soldiers,” Mr. Netanyahu said, in a message directed at Mr. Guterres.

The U.N. force has rejected Israel’s calls to leave its positions in southern Lebanon. Mr. Guterres does not have authority over UNIFIL, whose presence is mandated by the U.N. Security Council.

United Nations peacekeeping forces have been in southern Lebanon since 1978. The mission includes over 10,000 civilian and military personnel from 50 countries who are assigned to prevent border violations between Lebanon and Israel over a 75-mile stretch referred to as the Blue Line.

In an overnight call with Israeli Minister of Defense Yoav Gallant, U.S. Defense Secretary Lloyd J. Austin III “reinforced the importance of Israel taking all necessary measures to ensure the safety and security of UNIFIL forces and Lebanese Armed Forces,” the Pentagon press secretary, Maj. Gen. Pat Ryder, said in a statement.

The episode on Sunday was the latest in a series of Israeli challenges to the peacekeeping force since invading southern Lebanon in late September.

On Saturday, UNIFIL reported that Israeli soldiers had blocked peacekeepers’ passage through an area northeast of Ramyah, prompting the mission to issue its fourth warning in recent days to Israel and other parties “to steer clear of the mission’s premises and operations.”

“UNIFIL’s mandate provides for its freedom of movement in its area of operations,” it said.