The UN's food agency has gained access to grain silos in Yemen's port city of Hodeidah, which were cut off for months by rebels.
The World Food Programme is assessing how much of the wheat can be salvaged to feed starving civilians in the country.
The UN agency's spokesman, Herve Verhoosel, said a technical team visited the Red Sea Mills on Sunday for the first time since February.
The storage centre held about 51,000 tonnes of wheat – enough to feed 3.7 million people for a month – when the site became inaccessible because of fighting in September.
Four years after the Iran-backed Houthi rebels began their insurrection, the Arab world's poorest country has been driven to the brink of famine, creating what the UN says is the world's worst humanitarian crisis.
They are battling against forces loyal to the internationally recognised government of President Abdrabu Mansur Hadi, supported by an Arab Coalition.
The UN agency said its team concluded in February that it might be able to salvage about 70 per cent of the wheat in Hodeidah.
"More than two months have passed since that assessment and the wheat will have most likely further deteriorated in quality, particularly given the hot weather," Mr Verhoosel said.
A spokesman for the government forces in Hodeidah said that the UN officials were trying to get the mills working again as soon as possible.
“The UN team included experts from the WFP and the UN anti-mines programme,” said Col Wathah Al Dubaish, who travelled with the UN officials.
The team was accompanied by 28 mill employees, mostly engineers who arrived to do maintenance work on the silos, which were damaged by Houthi shelling.
“The UN team agreed with the executive manager of the mills to resume operations as soon as possible," Col Al Dubaish said.
"They agreed that within 10 days the mill workers would fumigate the rotten part of the wheat, which will be taken as food for cattle, while the good part will be distributed to the starving people."
The UN's attempts to ease Yemen's humanitarian crisis and resolve the conflict now hinge on a stalled peace agreement in Hodeidah, the entry point for 70 per cent of imports and humanitarian aid.
The warring sides have agreed to withdraw their forces from the city and its ports, but are divided over who will be in control when they pull out.
The UN-brokered deal reached in Sweden in December was vague on that point, saying only that a "local force" would take over.
Col Al Dubaish said UN envoy Martin Griffiths made another visit to the rebel-held capital, Sanaa, on Sunday "in a desperate attempt to push them to implement the first phase of the withdrawal from the key ports in Hodeidah".
He said the unannounced visit came after the UN-appointed head of the joint panel to oversee the withdrawal, Michael Lollesgaard, told government representatives on May 1 that the rebels were refusing to pull out from the ports of Al Saleef and Ras Issa under a modified plan to which they had agreed on April 29.
"So Mr Griffiths is back in Sanaa for the sixth time to convince the rebels to implement the first phase of the withdrawal as agreed," Col Al Dubaish said.
He said the joint government forces in Hodeidah would not keep waiting for the UN to convince the Houthis to seriously engage in the peace process and had told Mr Lollesgaard that they would act to protect thousands of civilians being subjected to continuous Houthi ceasefire breaches.
“We will wait for the Yemen Quartet [the US, UK, UAE and Saudi Arabia], which is going to meet in Aden in May 15, to see what is the latest decision regarding the Houthi refusal to implement the Stockholm Agreement," Col Al Dubaish said.
"Otherwise, we will launch a last push to take full control of Hodeidah."
