GENEVA (Reuters) - The top United Nations humanitarian official called on Monday for Gulf countries to help avert mass starvation in Yemen, where two years of war have left millions at risk of famine.

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Stephen O’Brien, U.N. Emergency Relief Coordinator, spoke in an interview a day ahead of a major conference where the U.N. is seeking $2.1 billion for Yemen this year.

The world body has received only 15 percent toward that appeal, none of it from regional countries, U.N. records show.

Yemen is reeling from conflict between Houthi rebels, aligned with Iran, against a Western-backed, Saudi-led coalition that is carrying out air strikes almost daily. At least 10,000 people have been killed in the fighting.

Some 17 million of Yemen’s 26 million people lack sufficient food and at least three million malnourished children are in “grave peril”, O’Brien said.

“This is rapidly becoming the world’s worst humanitarian disaster,” he told Reuters.

“I would urge the region in particular to step up to support the Yemeni people caught up in this conflict.”

U.N. aid agencies are reaching more than 5 million Yemenis “despite all the bureaucratic obstacles and the difficulties of access including at the ports”, O’Brien said.

The United Nations has already declared famine in parts of South Sudan and warned of looming famine in Somalia, South Sudan and Yemen.

Oxfam called on donor nations to step up life-saving assistance rather than providing arms to fuel the deepening conflict.

The British aid agency also said the international community must send a clear message that a coalition attack against Hodeidah, the strategic Red Sea entry point for some 70 percent of Yemen’s food imports, would be “totally unacceptable”.

Residents of Hodeidah, a city of 1.1 million, are concerned about a “possible escalation”, said Majd Farhat, head of the International Committee of the Red Cross (ICRC) sub-delegation there.

The ICRC has diverted its imports from Hodeidah port to bring cargo to Sanaa airport and possibly soon by land from Oman, he told reporters by Skype.

The agency is doubling its Yemen budget to 90 million Swiss francs ($90 million) and sending a second team of surgeons.

Alexander Ventura, head of Yemen’s mission for Medecins Sans Frontieres (MSF), said: “The health system is on the verge of collapse and medical services are under fire.”