The U.N. special envoy for Yemen warned Wednesday that conflict in the Arab world's poorest nation is intensifying daily, with terrorist groups expanding, 14 million people in desperate need of food and the worst cholera epidemic in the world.

Ismail Ould Cheikh Ahmed called on all parties "to act for the sake of peace," stressing that "their excuses are unacceptable and their justifications are unconvincing, especially when the solutions are in plain sight."

"The opportunity to reach peace is not yet lost," he told the Security Council. But "the political leadership must recognize that the continuation of the war can only lead to more human and physical loss, and complicate crucial questions on the future of the country, including the grievances of the south."

Yemen, which is on the southern edge of the Arabian Peninsula, has been engulfed in civil war since September 2014, when Houthi Shiite rebels swept into the capital of Sanaa and overthrew President Abed-Rabbo Mansour Hadi's internationally recognized government.

In March 2015, a Saudi-led coalition, backed by the United States, began a campaign against Houthi forces allied with ousted President Ali Abdullah Saleh in support of Hadi's government. Since then, the Iranian-backed Houthis have been dislodged from most of the south, but remain in control of Sanaa and much of the north.

In the southern part of the country, the United Arab Emirates, which is part of the Saudi-led coalition, has set up its own security forces, running virtually a state-within-a-state and fueling the south's independence movement.

U.N. humanitarian chief Stephen O'Brien said the warring parties and their outside backers should feel "deeply guilty" at driving a worsening conflict that has exposed millions of Yemenis civilians "to unfathomable pain and suffering" — including 7 million people now "on the cusp of famine" and more than 320,000 suspected cholera cases. He urged the Security Council to "lean much more heavily and effectively on the parties, and those outside Yemen who are leading this policy and action."

O'Brien said suspected cholera cases have been reported in nearly all the country's districts and at least 1,740 people have already died.

The $2.1 billion humanitarian appeal for Yemen is only 33 percent funded, and the response to the cholera epidemic requires an additional $250 million, of which just $47 million has been received, he said. "This cholera scandal is entirely man-made by the conflicting parties and those beyond Yemen's borders who are leading, supplying, fighting and perpetuating the fear and fighting," O'Brien said. "Just for the sake of reaching all the millions with cholera vaccines, the people of Yemen need stability so we can reach them at all."

The Security Council called on the parties "to immediately agree on the modalities for a durable cessation of hostilities" and to resume peace talks. It also called for "the immediate mobilization of additional funds to cover acute humanitarian needs," including for the rapidly spreading cholera epidemic.