The United Nations on Sunday called on Israel to immediately allow aid into Gaza, hours after it suspended humanitarian deliveries into the war-battered territory as talks on a truce extension appeared to hit an impasse.

Israel stopped the entry of all goods and supplies into the Gaza Strip on Sunday and warned of “additional consequences” if Hamas doesn’t accept a new proposal to extend a fragile cease-fire. Hamas accused Israel of trying to derail the existing ceasefire agreement and said its decision to cut off aid was “cheap extortion,

The first phase of the Israel-Hamas ceasefire, which included a surge in humanitarian assistance, expired on Saturday. The two sides have yet to negotiate the second phase, in which Hamas was to release dozens of remaining hostages in return for an Israeli pullout and a lasting ceasefire.