The United Nations and its partners have launched the 2021 humanitarian response plan for Yemen that seeks 3.85 billion U.S. dollars for urgent, life-saving aid for more than half of Yemen's war-torn population, a UN spokesman said on Wednesday. While about 16 million people need urgent help, 20.7 million Yemenis need some humanitarian assistance, including 12.1 million people in acute need, said Stephane Dujarric, the chief spokesman for UN Secretary-General Antonio Guterres. The United Nations estimates Yemen's population at more than 30 million people. "Yemen continues to be the world's worst humanitarian crisis and the largest aid operation," Dujarric said. "Famine is stalking the nation, with more than half the population facing acute food insecurity and record levels of acute malnutrition among children under 5." The spokesman noted that last year's plan was only 56 percent funded and some critical programs had to be closed as a result. "We are doing everything we can to help, but we need adequate funding as needs continue to rise," he told a regular briefing. "At the high-level pledging event that took place in early March, donors pledged only 1.7 billion U.S. dollars for the response -- that's less than half what is required (for 2021)." "The secretary-general said the pledges represent at best a down payment," Dujarric recalled. "We urge donors to quickly disburse their pledges and scale up funding for the humanitarian response to save lives. And if people have not yet pledged, it is never too late to do so."