United Nations Secretary-General António Guterres invoked Article 99 of the U.N. charter on Wednesday for the first time. He cited a “severe risk of collapse of the humanitarian system in Gaza” as the war rages on between Israel and the militant group Hamas.

In a letter to José Javier De la Gasca Lopez Domínguez, the current U.N. Security Council president, Guterres said he expects “public order to completely break down due to desperate conditions, rendering even limited humanitarian assistance impossible.”

The invocation of Article 99 allows the U.N. secretary-general to bring the attention of the security council to “any matter which in his opinion may threaten the maintenance of international peace and security,” per the U.N.

Guterres has called for a ceasefire.