The ebola outbreak in West Africa has killed more than 1,552 people out of 3,069 known cases in four countries and "continues to accelerate", the World Health Organisation (WHO) said on Thursday.

The epidemic in the region, the deadliest since the disease was first discovered in 1976, has killed nearly as many people as all the previous known outbreaks combined.

"More than 40 percent 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.

The WHO is later due to launch a new strategic plan for tackling the spread of the virulent disease.

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.

The disease has overwhelmed West Africa's already fragile health infrastructure. On Wednesday, the head of the African Development Bank said it was causing enormous damage to the economies of the region.

In another Reuters report, WHO said funds up to $490 million was needed to combat ebola over the next six month. – Reuters