An Israeli airstrike on a Gaza hospital Sunday killed four people and wounded another 17, WHO chief Tedros Adhanom Ghebreyesus said in a post on X, formerly Twitter.

The strike at Al-Aqsa hospital was witnessed by a World Health Organization team sent there to assess needs and to collect incubators for the north of Gaza, Tedros wrote. Israel's military denied that the hospital was damaged.

"A WHO team was on a humanitarian mission at Al-Aqsa Hospital in Gaza, when a tent camp inside the hospital compound was hit by an Israeli airstrike today," the WHO chief wrote.

He gave no details of the victims, but added: "WHO staff are all accounted for."

In a message posted on X, the Israeli army said one of its planes "struck an operational Islamic Jihad command center and terrorists positioned in the courtyard of the Al-Aqsa Hospital in the area of Deir al Balah.

"Following the precise strike, the Al-Aqsa hospital building was not damaged and its function was not affected," it added.

Tedros renewed his appeal for patients, health professionals and aid workers to be protected during the conflict, and for attacks on hospitals to stop.

"We again call for protection of patients, health personnel and humanitarian missions," he added.

"The ongoing attacks and militarisation of hospitals must stop. International humanitarian law must be respected."

Tedros urged all parties to the conflict to comply with the UN Security Council resolution calling for a ceasefire.

Since an unprecedented October 7 attack Hamas launched out of the Gaza Strip, Israel has said it will destroy the movement and has relentlessly bombed the Palestinian territory.

There are 10 hospitals in the Gaza Strip still functioning at a minimum level, compared to 36 before the start of the war, according to the WHO

As well as air strikes there has also been fierce ground fighting in and around hospitals in the territory, where many Gazans fleeing the violence have taken shelter inside the buildings.