Shifa Hospital said the dead and wounded were among crowds massed at the Zikim Crossing, the main entry point for humanitarian aid to northern Gaza.

Israel’s retaliatory offensive has killed more than 60,000 Palestinians, according to Gaza’s Health Ministry. Its count doesn’t distinguish between fighters and civilians. The ministry operates under the Hamas government. The U.N. and other international organizations see it as the most reliable source of data on casualties.

The U.N. is due to start vaccinating some 640,000 children in the territory against polio, relying on daily eight-hour pauses in fighting.