Yemen faces 'largest famine in decades' if Saudi-led blockades continue
UN aid chief Mark Lowcock told reporters in Sweden that the humanitarian disaster could claim "millions of victims" if no changes are made.
"I have told the council that unless those measures are lifted... there will be famine in Yemen," Lowcock said after a closed-door UN meeting.
"It will be the largest famine the world has seen for many decades with millions of victims."
The UN's warning follows the Saudi-led military coalition's announcement on Monday that all air, sea and land ports to Yemen had been closed.
The coalition, which is backing the government of President Abedrabbo Mansour Hadi, said the move was made to Iranian-supplied arms from reaching Houthi rebels.
The tightened restrictions are likely to exacerbate deteriorating conditions in Yemen, where around seven million people are living on the brink of famine and and a 'man made' cholera outbreak has infected around 900,000.
Lowcock, who visited Yemen last month, urged for the "winding down of the blockade... so that we can save the lives of those people".
He added that UN humanitarian flights had not been given access to Yemen since Monday.
More than 10,000 people have been killed since the Saudi-led coalition intervened in Yemen in 2015 to support President Hadi against the Houthis.
Rights groups have accused all sides in Yemen's war of perpetrating war crimes and have long criticised the blocking of vital aid for Yemen's civilians.
Lowcock urged that aid flights into Yemen be allowed to resume with assurances from the Saudi-led coalition that there will be no further disruption to aid efforts.