DUBAI (Reuters) - There is a “very real probability” the new coronavirus is circulating in Yemen, the United Nations said on Tuesday, warning that an aid funding shortfall would compromise efforts to combat the virus in one of the most vulnerable countries.

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The war-damaged nation, whose population has been weakened by widespread hunger and disease, has reported one laboratory-confirmed COVID-19 case but due to inadequate testing and a shattered health system aid groups fear a devastating outbreak.

The office of the U.N. aid chief in Yemen said that based on transmission patterns in other countries and given 17 days have passed since Yemen reported its first case, “agencies are warning there is now a very real probability that the virus has been circulating undetected and unmitigated within communities”.

“This increases the likelihood of a surge of cases which may quickly overwhelm health capacities,” it said in a statement.

The case announced on April 10, a 60-year-old port official, has since recovered and tested negative for the virus, Yemen’s coronavirus committee said on Monday.

But authorities told Reuters they have been unable to track down “patient zero”, an important step in tracing people potentially exposed to infection and containing an outbreak.

Yemen is already grappling with the world’s largest humanitarian crisis after five years of war between a Saudi-led coalition and the Houthi group that ousted the internationally recognised government from power in the capital, Sanaa.

Around 80% of Yemen’s population, or 24 million people, rely on aid, and 10 million are facing famine. Yemen has the world’s fourth highest internally displaced population and healthcare is scarce in rural areas.

Under such conditions the virus could spread rapidly, and the funding gap is compounding risk. The statement said 31 of 41 major U.N. humanitarian assistance programmes will scale-down or stop in coming weeks without more money.

One major donor, the U.S. Agency for International Development, cut funding last month over concerns that Houthi authorities are hindering aid distribution. The group, which controls most major urban centres, has dismissed the charges as baseless.

In mid-April the World Food Programme (WFP) said it had halved food aid to Houthi-controlled areas.

Refugee agency UNHCR said on Tuesday it received only 28% of funding required this year and needs $89.4 million to assist more than 3.6 million displaced people, alongside foreign refugees and host communities.

A senior U.S. official recently told Reuters the United States is preparing a “substantial contribution” to help Yemen’s coronavirus efforts.