Polio is spreading fast in Pakistan and Afghanistan.
A report presented to the World Health Organisation's annual assembly said warfare is the biggest barrier to eradication in Pakistan and Afghanistan.
According to the report, the number of children found to be paralysed there surged in the second half of last year.
The Global Polio Eradication Campaign said on Thursday that low immunisation rates in Nigeria have caused the virus to spread to eight of its neighbours: Benin, Burkina Faso, Chad, Cote d'Ivoire, Ghana, Mali, Niger and Togo - where it was previously wiped out.
The report also stressed "the fragility of progress" against the virus in India.
