The UN special envoy to Yemen warned that grain stores in Hodeidah were in danger of rotting if access to the stocks was not given.
Martin Griffiths spoke of the urgency of obtaining access to the stores in the Houthi-controlled port city.
The World Food Program grain stores at the Red Sea Mills are enough to feed 3.7 million people for a month and have been inaccessible for more than five months, Martin Griffiths said on Monday.
Yemen's almost four-year war has brought millions of people to the brink of famine.
The UN is pushing for the implementation of a ceasefire and troop withdrawal from Hodeidah, the main entry point for most of Yemen's imports, agreed in December in Sweden.
Accessing the 51,000 tonnes of UN wheat and milling equipment is a key aim of ongoing peace talks.
Yemen's conflict pits the Iran-backed Houthi movement against a Saudi-led coalition trying to restore the government of Abdrabu Mansur Hadi after it was ousted by the rebels in 2014.
Negotiations between the warring parties last week produced what the UN called a "preliminary compromise" on how to withdraw troops, although the deal has not yet finally agreed.
Mr Griffiths said he was encouraged by the recent engagement of all sides to find a way of accessing the mills.
"We emphasise that ensuring access to the mills is a shared responsibility among the parties to the conflict in Yemen. With safe, unfettered and sustained access, the United Nations can make this urgently needed food available to people in need," the UN said.
The joint statement from Mr Griffiths and UN aid chief Mark Lowcock said the UN was increasing its operations to provide food assistance to nearly 12 million people across Yemen.
