The International Committee of the Red Cross said 22 people were killed in a shell attack Friday that damaged its Gaza office, which is surrounded by hundreds of displaced persons living in tents.
The ICRC did not say who fired the "heavy calibre projectiles" but in a statement on social media platform X said the shells "damaged the structure of the ICRC office".
It said 22 bodies and 45 wounded had been taken to a nearby Red Cross field hospital after the shelling, and there were "reports of additional casualties".
The health ministry in the territory said there were 25 dead and 50 injured in the shelling which it blamed on Israel. The ministry said Israeli shelling had "targeted the tents of the displaced in the Al-Mawasi area" which is around the ICRC base.
An Israeli army spokesman did not acknowledge any role in the incident but said it was "under review".
"An initial inquiry conducted suggests that there is no indication that a strike was carried out by the IDF in the humanitarian area in Al-Mawasi. The incident is under review," the spokesman told AFP.
The ICRC said: "Heavy-calibre projectiles landed within metres of the office and residences of the International Committee of the Red Cross on Friday afternoon."
"Firing so dangerously close to humanitarian structures, of whose locations the parties to the conflict are aware and which are clearly marked with the Red Cross emblem, puts the lives of civilians and Red Cross staff at risk," the body added.
"This grave security incident is one of several in recent days," it added.
"Previously stray bullets have reached ICRC structures. We decry these incidents that put the lives of humanitarians and civilians at risk."
The ICRC has made increasingly desperate calls for warring parties to respect international law and protect civilians caught in the midst of the conflict that erupted on October 7.
Calling on both sides to do more to protect civilians "regardless of which side they are on", ICRC head Mirjana Spoljaric said it was "the line between humanity and barbarity".