The Israeli military is gradually expanding its military action by intensifying airstrikes and sending additional ground troops to the Hamas-controlled Gaza Strip. Thousands of people have looted a UN agency's warehouses there amid serious shortages of water and food due to Israel's blockade.

Israeli forces continued their ground operation in the Gaza Strip on Sunday. A military spokesperson said it is "progressing through the stages of the war according to plan" and "gradually expanding the ground activity."

The military announced that its troops had killed a number of Hamas militants coming out of an underground tunnel near the Erez Crossing in the northern Gaza Strip.

Hamas said it had attacked Israeli forces in the north of the enclave and elsewhere.

Casualties of Israel's heavy bombardments are surging in Gaza. Health authorities in the strip said 8,005 people had been killed since the conflict began on October 7. They said the dead include 3,324 children and 2,062 women.

The United Nations Relief and Works Agency for Palestine Refugees, or UNRWA, said thousands of people had broken into its warehouses and distribution centers in the middle and southern parts of the Gaza Strip. The agency said flour and other daily necessities had been stolen.

The head of UNRWA's local office said the looting is a "worrying sign that civil order is starting to break down after three weeks of war and a tight siege on Gaza."

He described people there as "scared, frustrated and desperate."

The Palestine Red Crescent Society said it had received what it called "serious threats" from Israel to immediately evacuate Al-Quds Hospital in the northern part of the Gaza Strip.

The director-general of the World Health Organization, Tedros Adhanom Ghebreyesus, expressed deep concern about the warning.

He said in a social media post that "it's impossible to evacuate hospitals full of patients without endangering their lives."

The WHO chief also said that healthcare must always be protected under international humanitarian law.

US President Joe Biden spoke with Israeli Prime Minister Benjamin Netanyahu by telephone on Sunday.

The White House said Biden "reiterated that Israel has every right and responsibility to defend its citizens from terrorism."

It also said Biden "underscored the need to do so in a manner consistent with international humanitarian law that prioritizes the protection of civilians."

At least 1,400 people have been killed on the Israeli side, with more than 200 people held hostage in Gaza. Hamas continues to fire rockets, injuring people in Israel.