"Even as the United Nations expands its aid operations in Yemen in what remains the world's worst humanitarian crisis, reaching 12 million people with more than 250 humanitarian agencies, the drivers of the crisis continue to get worse," Lowcock told a Security Council meeting on the situation in Yemen.
"In fact, it often feels in Yemen that the more we achieve, the bigger and more complicated the problem becomes," he said.
Recounting gruesome instances of shelling and bombing casualties, he added that air strikes last week hit a United Nations supported water system for 12,000 people.
"With more than 30 active front lines, we can only hope that recent steps towards de-escalation will continue," he said, calling for a nationwide ceasefire and respect for obligations under international humanitarian law to protect civilians and civilian infrastructure.