A school in northern Gaza run by a UN agency came under attack on Saturday as Israeli forces continued their ground invasion.

Qatar-based Al Jazeera satellite television station reported that at least 50 people died in the Israeli strike at the Jabalia refugee camp. It said the number of casualties could rise, as the school was being used to house many displaced Palestinians.

Commissioner-General Philippe Lazzarini of the UN Relief and Works Agency for Palestine Refugees, or UNRWA, posted a message on social media. He said that he has been "receiving horrifying images & footage of scores of people killed and injured in another UNRWA school sheltering thousands of displaced people."

Lazzarini said the attacks must stop, and he called for an immediate humanitarian ceasefire.

Israel's military did not mention the attack, but it said that its troops are expanding their operations in the Jabalia area. It said one of Hamas's most significant strongholds is located in the region. The military also claimed that its forces have killed many Hamas militants who were operating in civilian areas.

There is growing concern that the conflict could spread, as the Israeli forces appear to be stepping up their attacks.

Health authorities in Gaza criticized the Israeli military for forcing people at Al-Shifa Hospital to evacuate. Al-Shifa is the largest hospital in the enclave. The Israeli forces raided the facility on Wednesday. They claimed that they were searching for Hamas's command and control center.

The health authorities noted that the lives of hundreds of patients and premature babies are still in danger. They said that the Israeli forces are responsible for the safety and lives of everyone in the hospital.

The Israeli military denied the Palestinian accounts. It claimed that it has been helping with the evacuations. It also claimed that the hospital asked it to do so.