The Houthis, who control Yemen's capital Sanaa, used diggers to break up sacks of maggot-ridden rice and flour bearing the logo of the UN's World Food Programme (WFP).
"This consignment of foodstuff was going off and was full of small insects... it wasn't even good for animals," said Houthi official Majed Sari.
A UN source said the aid had been intended for delivery to families in the city of Taiz in November 2018.
But it "ended up detained at a checkpoint for months and months", the source told AFP.
Yemen was already the Arab world's poorest nation when a Saudi-led coalition intervened in 2015 to prop up the government after the Houthis seized the capital Sanaa.
The conflict has since triggered widespread malnutrition and what the UN calls the world's worst humanitarian crisis.
But the WFP, which says it feeds around 11 million people a month in Yemen, halted distributions to Houthi-controlled territory in June following accusations of "diversion of food" meant for Yemeni civilians.
In early August, it reached a deal to resume deliveries after the Houthis offered guarantees concerning the beneficiaries, the UN agency said.
The war has left tens of thousands of people dead since the Saudi-led coalition intervened, according to UN figures.
Over three million people have been displaced and some two-thirds of the country's population are in need of aid, the world body says.
A WFP spokesperson told AFP that the agency distributes more than 130,000 metric tonnes of food each month in Yemen despite "operational challenges" linked to the complex conflict.
"WFP needs unimpeded access to all areas of the country so we can get food assistance to those who need it most," the spokesperson said.
Last week, the UN said it was "desperate" for funds in Yemen after being forced to stop aid programmes due to a cash shortage that threatens to reduce food deliveries.
Several programmes "have been forced to close in recent weeks and many large-scale projects designed to help destitute, hungry families have been unable to start," said Lise Grande, the UN's humanitarian coordinator for Yemen.
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