At least 18 people were killed in an Israeli air strike on a Gaza mosque early on Sunday, said Palestinian news agency WAFA.
The strike on the mosque, near the Al-Aqsa Hospital in Deir al-Balah in the central Gaza Strip, came as Israel's war in the Palestinian enclave approaches its first anniversary.
The initial death toll was five but eyewitnesses said the number of casualties could rise as the mosque was being used to house displaced people.
The Israeli military claimed in a statement it "conducted a precise strike on Hamas terrorists who were operating within a command and control center embedded in a structure that previously served as the 'Shuhada al-Aqsa' Mosque in the area of Deir al Balah."
Hamas has repeatedly denied Israeli accusations that it uses civilian infrastructure for its military activities, and Israel does not provide evidence for its claims.
Israel's military assault on Gaza has killed nearly 42,000 Palestinians, most of them civilians, according to Gaza's health ministry. It has also displaced nearly all of the enclave's 2.3 million people, caused a hunger crisis and led to genocide allegations at the World Court that Israel denies.
The war was sparked by the October 7 attack led by Hamas in southern Israel which resulted in the deaths of around 1,200 people, and some 250 taken hostage. Hamas says the attack was a response to decades of Israeli occupation, aggression and the Gaza siege.