KHAN YOUNIS, Gaza Strip — Israel bombed areas of southern Gaza where it had told Palestinians to flee to ahead of an expected ground invasion, killing dozens of people on Tuesday in retaliatory attacks it says are targeted at Hamas militants that rule the besieged territory.

Dozens of injured were rushed to hospitals after heavy attacks outside the southern cities of Rafah and Khan Younis, residents reported. Basem Naim, a senior Hamas official and former health minister, reported 27 people were killed in Rafah and 30 in Khan Younis.

An airstrike in Deir al Balah reduced a house to rubble, killing nine members of the family living there. Three members of another family that had evacuated from Gaza City were killed in a neighboring home. The dead included one man and 11 women and children. Witnesses said there was no warning before the strike.

The Israeli military said it was targeting Hamas hideouts, infrastructure and command centers. “When we see a target, when we see something moving that is Hamas, we’ll take care of it,” Lt. Col. Richard Hecht, an Israeli military spokesman, said.

President Joe Biden planned to travel to Israel on Wednesday to signal White House support for the country and to Jordan to meet with Arab leaders. U.S. Secretary of State Antony Blinken announced the trip early Tuesday in Tel Aviv during his second visit to Israel in less than a week amid fears that the fighting could expand into a broader regional conflict.

Meanwhile, truckloads of aid idled at Egypt’s border with Gaza as residents and humanitarian groups pleaded Monday for water, food and fuel for dying generators, saying the tiny Palestinian territory sealed off by Israel after last week’s rampage by Hamas was near total collapse.

In Gaza, hospitals were on the verge of losing electricity, threatening the lives of thousands of patients, and hundreds of thousands of Palestinians displaced from their homes searched for bread. Israel maintained punishing airstrikes across Gaza as a ground invasion loomed, while Hamas militants kept up a barrage of rocket attacks, and tensions mounted near the Israel-Lebanon border.

More than a week after Israel cut off entry of any supplies, all eyes were on the Rafah crossing, Gaza’s only connection to Egypt. Mediators were trying to reach a cease-fire that would let in aid and let out trapped foreigners. Israeli airstrikes forced the crossing to shut down last week, but it remained unclear Monday which of the regional actors was keeping the crossing closed.

Blinken, who returned to Israel after a six-country tour through Arab nations, said the U.S. and Israel had agreed to develop a plan to enable humanitarian aid to reach civilians in Gaza. There were few details, but the plan would include “the possibility of creating areas to help keep civilians out of harm’s way.”

“We share Israel’s concern that Hamas may seize or destroy aid entering Gaza or otherwise prevent it from reaching the people who need it,” Blinken said.

Israel evacuated towns near its northern border with Lebanon, where the military has exchanged fire repeatedly with the Iranian-backed Hezbollah group.

Speaking to the Israeli Knesset, Prime Minister Benjamin Netanyahu warned Iran and Hezbollah, “Don’t test us in the north. Don’t make the mistake of the past. Today, the price you will pay will be far heavier,” referring to Israel’s 2006 war with Hezbollah, which operates out of Lebanon.

Soon after he spoke, the Knesset floor was evacuated as rockets headed toward Jerusalem. Sirens in Tel Aviv prompted U.S. and Israeli officials to take shelter in a bunker, officials said.

Iran Says ‘Preemptive Action Possible’

Iran’s foreign minister, meanwhile, warned that “preemptive action is possible” if Israel moves closer to a ground offensive. Hossein Amirabdollahian’s threat followed a pattern of escalating rhetoric from Iran, which supports Hamas and Hezbollah.

This has become the deadliest of the five Gaza wars for both sides. At least 2,778 people have been killed and 9,700 wounded in Gaza, according to the Health Ministry there. More than 1,400 Israelis have been killed, the vast majority civilians massacred in Hamas’ Oct. 7 assault.

The Israeli military said Monday that at least 199 hostages were taken into Gaza, more than previously estimated. Hamas said it was holding 200 to 250 hostages, including foreigners whom it said it would free when it was feasible.

Also Monday, Hamas’ military wing released a hostage video showing a dazed woman having her arm wrapped with bandages. The woman, who identified herself in the video as Mia Schem, 21, rocked slightly as she spoke, the sound of explosions reverberating in the background. In her statement, Schem was taken from Kibbutz Reim, where she was attending a rave near the Israel-Gaza border. Hamas said she had undergone a three-hour operation.

The Israeli military said Schem’s family was told of her abduction last week, and officials dismissed the video as propaganda.

The plight of the hostage s has dominated the Israeli media since the attack, with interviews of their relatives playing almost constantly. Israeli officials have vowed to maintain the siege of Gaza until the hostages are released.

The head of Israel’s Shin Bet security service, in charge of monitoring militant groups, took responsibility for failing to avert Hamas’ surprise attack. As agency head, “the responsibility for that is on me,” Ronen Bar said.

“There will be time for investigation — now is a time for war,” he wrote in a letter to Shin Bet workers and their families.

The combination of airstrikes, dwindling supplies and Israel’s mass evacuation order for the north of the Gaza Strip has thrown the tiny territory’s 2.3 million people into upheaval and increasing desperation. More than 1 million have fled their homes, and 60% are now in the approximately 14-kilometer-long (8 mile) area south of the evacuation zone, according to the U.N.

The Israeli military says it is trying to clear civilians for their safety ahead of a major campaign against Hamas in Gaza’s north, where it says the militants have extensive networks of tunnels and rocket launchers. Much of Hamas’ military infrastructure is in residential areas.

Those fleeing northern Gaza still faced airstrikes in the south. Before dawn Monday, a strike in the town of Rafah collapsed a building sheltering three families who had evacuated from Gaza City. At least 12 people were killed and nine others remained buried under rubble, survivors said. The strike reduced the house to a vast crater blanketed with wreckage.

Hospitals are expected to run out of generator fuel in the next 24 hours, meaning life-saving equipment like incubators and ventilators will stop functioning and putting thousands of lives at risk, the U.N. said.

People grew increasingly desperate in their search for food and water. With taps dry, many have resorted to drinking dirty or sewage-filled water, risking the spread of disease.

More than 400,000 displaced people in the south crowded into schools and other facilities of the U.N. agency for Palestinians, UNRWA. But the agency can’t provide them supplies. UNRWA said it has only 1 liter of water a day for each of its staff members trapped in the territory.

“Gaza is running out of water, and Gaza is running out of life,” said UNRWA chief Philippe Lazzarini, calling for a lifting of the siege. “We need this now.”

The few operating bakeries had long snaking lines of people. Ahmad Salah in the city of Deir al-Balah said he waited 10 hours to get a kilo (2 pounds) of bread to feed 20-30 family members.

In northern Gaza, unknown numbers remained, either unwilling or unable to leave.

UNRWA said 170,000 people were sheltering at its schools in the north when the order to leave came. But it couldn’t evacuate them and doesn’t know if they remained. More than 40,000 have crowded in and around Gaza City’s al-Shifa Hospital, hoping it will be safe from bombardment.

Hamas urged people to ignore the evacuation order. The Israeli military on Sunday released photos it said showed a Hamas roadblock preventing traffic from moving south.

Doctors and many hospital staff have refused to evacuate, saying it would mean death for critically ill patients and newborns on ventilators. The aid group Doctors Without Borders said many of its personnel decided to stay to treat wounded. They ran out of painkillers, and staff reported “wounded screaming in pain,” it said.

On the Gaza side of the Rafah crossing, crowds of Palestinians with dual citizenship waited anxiously, sitting on suitcases or crouched on the floor, some comforting crying infants.

“They are supposed to be a developed country, talking about human rights all the time,” Shurouq Alkhazendar, whose two children are American citizens, said of the United States. “You should protect your citizens first, not leave them all alone suffering.”

After increasing cross-border exchanges with Hezbollah in the north, the Israeli military ordered residents to evacuate 28 communities within 2 kilometers (1.2 miles) of the Lebanese border.

“Israel is ready to operate on two fronts, and even more,” said Rear Adm. Daniel Hagari, a military spokesman.

Hezbollah released video showing snipers shooting out cameras on several Israeli army posts along the border, apparently to prevent Israel from monitoring movements on the Lebanese side.

The U.S. government began evacuating some 2,500 American citizens by ship from the Israeli port city of Haifa to Cyprus. Commercial airlines have largely stopped flying into Israel’s Ben-Gurion International Airport.