WHO chief Tedros Adhanom Ghebreyesus said four people were killed in an Israeli airstrike on al-Aqsa Hospital in Gaza.
A further 17 people were wounded in the attack.
A World Health Organization team witnessed the strike at the hospital during a mission to assess requirements and collect incubators in north Gaza.
“WHO staff are all accounted for,” he said in a statement posted to X.
Tedros renewed his appeal for patients, healthcare workers, and aid workers to be protected during the war and for attacks on hospitals to end.
“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,” he said. “The ongoing attacks and militarization of hospitals must stop. International humanitarian law must be respected.”
Tedros called for all parties to comply with the UN Security Council resolution for a ceasefire.
