GENEVA (Reuters) - The Ebola outbreak in West Africa has taken 1,552 lives out of 3,069 known cases in four countries and "continues to accelerate", the World Health Organisation (WHO) said on Thursday.

"More than 40 per cent of the total number of cases have occurred within the past 21 days. However, most cases are concentrated in only a few localities," the United Nations health agency said in a statement ahead of launching its new strategic plan for tackling the world's worst Ebola outbreak.

A separate Ebola outbreak in the Democratic Republic of Congo, identified as a different strain of the virus, is not included in the latest figures which cover Guinea, Liberia, Sierra Leone and Nigeria, it said.