GENEVA (Reuters) - The death toll from the Ebola outbreak in West Africa has risen to 6,331 in the three worst hit countries, with Sierra Leone overtaking Liberia as the country with the highest number of cases, World Health Organization figures showed on Monday.

The cumulative number of cases in Guinea, Liberia and Sierra Leone totalled 17,800, including 7,719 in Liberia and 7,798 in Sierra Leone, WHO said. On Friday, WHO put the three countries' combined death toll at 6,187, out of 17,517 cases.

Just over half the reported deaths were in Liberia, but the true toll in Sierra Leone, with an estimated fatality rate of 70 percent, is likely to be far higher than the figures show, WHO experts say.

(Reporting by Tom Miles; Editing by Susan Fenton)