Thousands of tonnes of food aid for war-ravaged Yemen have been diverted from the port of Aden because of heavy fighting there, U.N. officials said on Monday.

It is the latest setback for aid agencies trying to reach hundreds of thousands of desperate people in the Arabian peninsula's poorest country amid a Saudi-led bombing campaign against Houthi fighters.

The ship MV Amsterdam, carrying enough grain and other food aid to sustain 60,000 Yemenis for a month, was unable to dock in the southern port city of Aden because of fighting and was diverted to the port of Hudaydah, the U.N. World Food Programme said in a statement.

U.N. officials will try to move the food to Aden by road if the security situation allows, a WFP spokeswoman said.

Aden has been one of the hardest hit areas in more than two months of conflict, including heavy street fighting, between Saudi-backed forces trying to restore the exiled president and Shi'ite Muslim Houthi fighters.

"It's a humanitarian crisis," WFP spokeswoman Abeer Etefa told the Thomson Reuters Foundation by phone from Cairo. "The city has been cut off from supplies for a long time."

Aden residents have no running water or electricity, and food shops are empty because supplies have not been getting into the city, Etefa said.

Even before the latest violence, many Yemenis were going hungry. Yemen imports around 90 per cent of its food and an estimated 16 million people, more than 60 per cent of the population, need humanitarian assistance, the U.N.'s Food and Agriculture Organization (FAO) reported. – Reuters