"We deplore today's attack on the U.N.'s Khan Younis training center," Patel told a news briefing, calling it "incredibly concerning."

The Director of UNRWA Affairs in Gaza said that nine Palestinians were killed and 75 were injured when two tank rounds hit the building that was sheltering around 800 people in the southern Gaza Strip.

"Civilians must be protected, and the protected nature of UN facilities must be respected, and humanitarian workers must be protected so that they can continue providing civilians with the life-saving humanitarian assistance that they need," Patel said.

(Reporting by Humeyra Pamuk and Simon Lewis; Editing by Chizu Nomiyama)