The World Food Programme on Wednesday said it requires more than double the money raised for all United Nations agencies in Yemen this year to reinstate full food rations for millions in need.

Last June, the UN's food agency was forced to slash food aid for 13 million Yemenis by more than 50 percent as a funding squeeze compounded one of the world's worst humanitarian crises.

The UN raised only $1.2 billion for all its agencies in Yemen at a pledging conference in Geneva last month -- well short of the $4.3 billion target.

The WFP's "requirements for Yemen are $3 billion until the end of the year... to revert to full ration," Corinne Fleischer, the agency's regional director for the Middle East, North Africa and Eastern Europe, told a media briefing in Dubai.

It remains unclear how much will be allocated to the WFP, and if it will be enough to continue the scaled-back rations.

Yemen's conflict broke out in 2014, when Iran-backed Huthi rebels seized the capital Sanaa, prompting a Saudi-led coalition to intervene the following year to prop up the internationally recognised government.

Since then, the war has caused hundreds of thousands of deaths, both directly and indirectly, and pushed the nation to the brink of famine.

A truce that began on April 2 last year expired on October 2, but fighting has remained largely on hold since.

The UN says more than 21.7 million -- two-thirds of Yemen's population -- need humanitarian assistance this year. Its appeal aims to reach the 17.3 million most vulnerable people.