Israeli forces besieged hospitals and shelters for displaced people in the northern Gaza Strip on Monday as they stepped up their operations against Palestinian militants, residents and medics said.

Troops rounded up men and ordered women to leave the Jabalia historic refugee camp, they said. An Israeli airstrike on a house in Jabalia killed five people and wounded several others, medics said.

The UN Palestinian refugee agency UNRWA said Israeli authorities were preventing humanitarian missions from reaching areas in the north of the Palestinian enclave with critical supplies, including medicine and food.

"People attempting to flee are getting killed, their bodies left on the street," UNRWA head Philippe Lazzarini said on X.

Medics at the Indonesian Hospital told Reuters that Israeli troops stormed a school and detained the men before setting it ablaze. The fire reached hospital generators and caused a power outage, they added.

Health officials said they had refused orders by the Israeli army, which started a new incursion into the territory's north over two weeks ago, to evacuate the three hospitals in the area or leave the patients unattended.

Troops remained outside the hospital but did not enter, they said. Medics at a second hospital, Kamal Adwan, reported heavy Israeli fire near the hospital at night.

"The army is burning the schools next to the hospital, and no one can enter or leave the hospital," said one nurse at the Indonesian Hospital, who asked not to be named.

Palestinian health officials said at least 18 people had been killed in Jabalia and eight elsewhere in Gaza in Israeli strikes.

The Israeli military said in a statement it was operating against "terrorists and terrorist infrastructure" in the Jabalia area.