Health officials have detected three cases of polio in southern Niger, near the border with Nigeria, the health ministry said Friday, just months after a major UN vaccination operation.
Experts from Niger, the World Health Organization and the UN's children agency UNICEF have already arrived in the area to investigate.
Polio is a highly infectious viral disease which mainly affects young children and can result in permanent paralysis. There is no cure and it can only be prevented through immunisation.
In April, UN health workers vaccinated more than five million children in Niger against the disease including nearly 42,000 children in refugee camps in the Lake Chad region where Niger borders with Nigeria, Chad and Cameroon
Niger officials say most cases found in the country are imported from neighbouring Nigeria, from where many people have fled the attacks of Boko Haram jihadists.