The WFP said on Friday that it expects that as many as three million people in northern Yemen and 1.4 million in the south will be affected.
The UN said Yemen, the Arabian Peninsula's poorest country, is in the grip of one of the world's worst humanitarian crises after eight years of war.
Seventeen million Yemenis are suffering food insecurity, and one million women and 2.2 million children under five need treatment for acute malnutrition.
The WFP said that “a deeper funding crisis” for its Yemen operations from the end of September was forcing the agency “to make difficult decisions about further cuts to our food assistance programmes across the country in the coming months”.
“We are confronted with the incredibly tough reality of making decisions to take food from the hungry to feed the starving,” the WFP statement quoted Richard Ragan, its Yemen representative, as saying.
He said the agency was “fully cognisant of the suffering these cuts will cause”.
The WFP said it required $1.05 billion in funding for the next six months, only 28 per cent of which has been secured.
“Yemen will remain one of WFP's largest food assistance operations, but these cuts represent a significant reduction to the agency's programmes in the country,” it said.
“The funding shortages are happening at a time of more people becoming severely malnourished.”
The agency was forced to cut food aid for 13 million Yemenis by more than half in June last year because of a funding squeeze.
Yemen's conflict broke out in 2014, when Iran-backed Houthi rebels seized the capital Sanaa, prompting a Saudi-led coalition to intervene the following year to prop up the internationally recognised government.
Although fighting has remained largely on hold since a six-month truce expired in October, the UN said current hunger levels are unprecedented.
Hans Grundberg, UN special envoy for Yemen, told the Security Council this week that prospects of a peaceful resolution to the conflict were being undermined by continued threats and economic warfare between the rebels, who control much of the north, and the government, which controls most of the south.