Officials have discovered four cases of polio in the Yemeni port city of al-Hudaydah and suspect the disease came from nearby countries, the World Health Organization (WHO) said on Friday.

These are the first reported cases of polio in Yemen since 1996.

Health officials are searching for other cases in the Arab state as scientists examine the virus’ genetic composition to see whether it is indigenous and signals a new outbreak or stems from another country.

“We are now investigating the origin of this virus and whether there are more cases in Yemen,” WHO spokeswoman Christine McNab told a news briefing. “We don’t know whether this is an importation but indications are that it is.”

The crippling disease, target of global eradication efforts since 1988, is considered endemic in six countries: Nigeria, India, Pakistan, Niger, Afghanistan and Egypt.

Yemen is the 15th previously polio-free country, including 13 in Africa, to report an outbreak since northern Nigeria suspended vaccinations in late 2003 for 10 months, sparking an epidemic that has spread across Africa.

The case marks a setback for the Geneva-based WHO, the United Nations’ main health body, which has stepped up its campaign to stop polio transmission by the end of this year despite the rising number of cases.

Polio is a virus that affects mainly children under the age of five and can cause irreversible paralysis in a matter of hours.

Yemen launched a nationwide campaign to vaccinate children against the disease only last week, McNab said. “We hope that this will help contain this outbreak,” she said.

McNab said the WHO needed $50 million in additional funding before June if it was to succeed in wiping out the virus by the end of 2005.