The World Health Organisation (WHO), battling to eradicate polio world-wide by the end of the year, confirmed on Tuesday that the disease had resurfaced in Cameroon and Benin.
The UN health agency said one case had been identified in each of the West African states, and had spread there from neighbouring Nigeria.
Once one of the world's most devastating and widespread diseases, polio is now endemic in only six countries - India, Pakistan, Nigeria, Afghanistan, Niger and Egypt - but stamping it out completely has proved difficult.
Over 650 cases were reported in 2003, Nigeria topping the list with 300, followed by India with 214 and Pakistan with 96. But the total was sharply down on the 1,918 recorded in 2002.
The Geneva-based organisation has called a meeting on Thursday of health ministers and senior officials from the six countries and three other states - Ghana, Chad and Burkina Faso - to which the disease has been imported in recent months from Nigeria.