Guinea has suffered the highest death toll with 358 fatalities out of 485 confirmed Ebola cases so far. Sierra Leone has had the largest number of cases, 646 overall, and 273 deaths, while Liberia has had 468 cases and 255 deaths.
Nigeria, the latest country to import the disease, has had four cases, of which three are classed as 'probable' Ebola and one as 'suspected', the Geneva-based agency said in a statement.
The case of Patrick Sawyer, an American who died shortly after flying from Liberia at Lagos airport via Togo and Ghana, is still classed as "probable". The WHO previously said it had not managed to check his sample because courier companies had refused to transport it to the Institut Pasteur in Dakar.
The other two probable Ebola cases in Nigeria were a health-care worker and a Nigerian who had been to Guinea, WHO said.
Nigeria itself has reported only the cases of Sawyer and, on Monday, one of the doctors who treated him.
A senior official in the Lagos state Ministry of Health declined to comment on the discrepancy.