Yemen’s war has left hundreds of thousands dead and created what the United Nations calls the world’s worst humanitarian crisis.

The temporary ceasefire, which took effect in April and has twice been renewed, is set to expire on Sunday, despite a recent attempt by the UN envoy for Yemen, Hans Grundberg, to extend it.

“Over the past six months, we haven’t seen any serious willingness to address humanitarian issues as a top priority," the Houthis said in a statement.

The warring sides have largely ceased fire and the truce has also allowed for some humanitarian measures, but both sides accuse each other of failing to live up to their commitments.

US ambassador to Yemen Steven Fagin said in a tweet on Saturday that he was “concerned about the lack of progress” in talks to extend the truce.

“I call on the parties not to squander the progress of the last six months,” he added, urging an “extension and expansion of the truce.”