The current Ebola outbreak in West Africa could infect more than 20,000 people, the World Health Organisation (WHO) said.
The United Nations health agency issued a strategic plan to combat the oubreak in four West African nations where it said the actual number of cases could already be two to four times higher than the reported 3,069. The death toll stands at 1,552.
"This roadmap assumes that in many areas of intense transmission the actual number of cases may be 2-4 fold higher than that currently reported. It acknowledges that the aggregate case load of Ebola Virus Disease could exceed 20,000 over the course of this emergency," the WHO said.
(READ MORE: WHO warns of "shadow zones" and unreported Ebola cases)
The deadly outbreak that began in Guinea in March and has spread to neighbouring Liberia and Sierra Leone as well as to Nigeria requires a massive and coordinated international response, the WHO said.
A separate outbreak of Ebola in Democratic Republic of Congo identified as a different strain, is not included in its toll.
"Response activities must be adapted in areas of very intense transmission and particular attention must be given to stopping transmission in capital cities and major ports, thereby facilitating the larger response and relief effort," the WHO said.
The virus is still being spread in a "substantial number of localities", aggravating fragile social and economic conditions and has already killed an unprecedented number of health workers, the agency said.
A wider UN-led plan being launched by the end of September is "expected to underpin support for the increasingly acute problems associated with food security, protection, water, sanitation and hygiene, primary and secondary health care and education, as well as the longer-term recovery effort that will be needed," the WHO said.