Under-Secretary-General Mark Lowcock told reporters on Monday at the world body's headquarters in New York that there was a "dramatic deterioration" of the crisis in Yemen, where 15 percent more of the population faces hunger than last year, CBS News reported.
Aid organizations have not been able to use the Red Sea port of Hudaydah and have instead been forced to bring supplies for the north of the country through the southern port of Aden.
"Hudaydah port is a lifeline," Lowcock said on Monday.
"It's not the only port, but our position is that we want all the land ports and all the seaports to be open."
Ending the Saudi aggression on the key port city has been discussed at truce talks in Rimbo, Sweden, between the Houthi Ansarullah movement and the Saudi-backed forces loyal to fugitive former president Abd Rabbuh Mansur Hadi.
"The vast majority of the people in Yemen are in Houthi-controlled areas, and Hudaydah is the way you get food into those people," Lowcock said.
UN special envoy Martin Griffiths has been positive about the talks. Meanwhile, an inter-agency report from the UN's humanitarian divisions described a crisis.
"For the first time, food security assessments have confirmed the worst levels of hunger in Yemen," the report said.
Henrietta Fore, executive director of the UN children agency, said, "In a war waged by adults, it is the country's children who suffer first and suffer most ... thousands of Yemeni children could die from severe malnutrition if conditions, including conflict and economic crisis, do not improve soon."
And World Food Program Executive Director David Beasley was more concerned than he has been, having traveled to Yemen on several occasions. "This report is an alarm bell that shows hunger is rising," Beasley said, "and we need a massive increase in aid and sustained access to all areas in Yemen in order to rescue millions of Yemenis."