The World Food Programme said on Thursday that it had begun partially suspending aid to Houthi-controlled Sanaa, Yemen’s capital.
The agency has accused the Houthis of stealing food assistance and said suspension would initially be confined to Sanaa city.
The UN agency delivers monthly rations or money to 10.2 million people in Yemen's population of 26 million.
“WFP’s priority remains to feed the hungriest children, women and men of Yemen,” the agency said.
“But some individuals seek to profit by preying on the vulnerable and diverting food away from where it is most needed.”
The programme said 850,000 people would be affected but that it remained “optimistic that a way forward can be found”.
"We are ready to immediately resume food distributions once we reach agreement on an independent beneficiary identification exercise and the roll out of a biometric registration system," it said.
WFP partially suspends aid in Houthi controlled areas after failure:
— د. أنور قرقاش (@AnwarGargash) June 20, 2019
"to introduce controls to prevent the diversion of food away from some of the most vulnerable people in Yemen,"
"some individuals seek to profit by preying on the vulnerable."
On Monday, the UN agency's food programme director David Beasley told the UN Security Council that the Houthi leadership failed to address the problem of stealing food over the past 18 months.
“Let me be crystal clear: children are dying right now because of this,” Mr Beasley said.
“There are those who stand to make a profit and they will do everything to obstruct and delay.”
Coalition-backed forces have retaken much of the south but Iran-backed Houthi rebels seized Yemen’s capital in 2015 and most of the central highlands remain in rebel hands.
On Tuesday, Yemen’s internationally recognised government said it wanted to avoid a military battle for Sanaa.
Information Minister Moammar Al Eryani said on a visit to Washington this week that his government “wants to spare Yemenis’ blood”.
“The government troops are 20 kilometres from Sanaa and have been there for a year," he said.
"We are capable of achieving victory but we don’t want to conquer it militarily for the sake of the Yemenis. We want a political solution and we are serious about the peace process.”
His comments came after the death toll in the country’s civil war reached 91,600.
