"The incident is a dramatic and disturbing escalation in a series of demonstrations that have taken place over the past week," the U.N. Relief and Works Agency for Palestine Refugees in the Near East said Thursday in a statement.
"These demonstrations affect our ability to provide much-needed service to the Palestine refugees in Gaza and -- because they also targeted the Gaza headquarters building -- our operations in the West Bank, Jordan, Lebanon and Syria," the statement said.
The agency said the centers would remain closed until it received assurances of safety and security for its staff and property, the BBC reported.
Protesters stormed the program's headquarters in Gaza after the agency said would reduce its cash-assistance program because of budget shortages.
The U.N. Relief and Works Agency for Palestine Refugees said its large-scale food distribution program that serves more than 800,000 people "will continue unchanged."
The agency said financial support for its programs to help Palestinian refugees hasn't kept pace with the deepening poverty of those needing its services, the BBC said. The unit said it has a deficit in excess of $67 million.
Robert Turner, director of the U.N. agency's operations in Gaza, said what happened Thursday was "completely unacceptable."
"The situation could very easily have resulted in serious injuries to [U.N. Relief and Works Agency for Palestine Refugees] staff and to the demonstrators," he said. "This escalation, apparently pre-planned, was unwarranted and unprecedented."