GENEVA — The World Health Organization said on Thursday that the Ebola epidemic was still accelerating and could afflict more than 20,000 people — almost seven times the current number of reported cases — before it could be brought under control.

The dire forecast was made as the health organization reported that the number of known cases and fatalities had risen once again. The organization also acknowledged that in areas of intense transmission “the actual number of cases may be two to four times higher than that currently reported.”

The outbreak “continues to accelerate,” the organization said.

According to the latest figures released by the health organization on Thursday, the total cases had risen to 3,069, with 1,552 deaths, in four West African countries: Guinea, Liberia, Sierra Leone and Nigeria.