The U.N.'s children's agency says an outbreak of polio in Sudan is spreading to other African countries and beyond, threatening millions of children.

Sudan had been free of polio for three years before the current outbreak began there last May.

Since then, the crippling disease that mainly affects young children has spread rapidly across Africa's largest country, infecting at least 124 people in 17 states.

Speaking to VOA from Wau in southern Sudan, UNICEF's representative to Sudan, Joanna Van Gerpen, says the situation is becoming more alarming. "There has been at least one, and I think there may be two or three more cases, that have been exported by Sudan to neighboring countries," she said..

Ms. Van Gerpen says a polio case in Saudi Arabia has been positively traced back to a strain from Sudan.

On Monday, two children in Ethiopia were diagnosed with the disease, marking the first time the virus has been reported in that country in four years. Ms. Van Gerpen says UNICEF believes the polio virus in Ethiopia also came across the border from Sudan.

"There are enough cases that are circulating in Sudan that it is now considered endemic to the country, the wild polio virus is present here in Sudan," she said. "So, it is no longer a case of just importation."

The first polio virus detected in Sudan originated in Nigeria, which now accounts for 60-percent of the world's polio cases. Health officials believe the virus made its way east from Nigeria to Chad, and then into the Darfur region of western Sudan, where a bloody, two year-old civil war has caused hundreds of thousands of people to scatter within and outside the country.

Ms. Van Gerpen says officials in Khartoum, as well as rebel leaders in Darfur, are cooperating with U.N. health officials in a massive countrywide campaign, aimed at vaccinating more than seven-million Sudanese children against polio.

"We have had some very good examples of cooperation," added Ms. Van Gerpen. "But it has not been complete, and that means you do have pockets where the polio virus could still be in circulation."

Ethiopia is the 14th country, 13th in Africa, to record imported cases of polio since an outbreak began in Nigeria 18-months ago.

East of Sudan, Eritrea, is watching carefully for signs of an outbreak. World Health Organization officials in the capital, Asmara, say a suspected case of polio there turned out to be negative.

Meanwhile, a vaccination campaign against polio was launched last week in three East African countries bordering Sudan. Several international agencies and government and non-government organizations in Ethiopia, Kenya, and Uganda are involved in the drive to immunize all children under the age of five.

The polio virus usually attacks the nervous system of children, causing paralysis and sometimes death from respiratory problems.