WHO assistant director-general Dr. Bruce Aylward gave the figure during a news conference Tuesday.
Aylward said that the 70 per cent death rate was "a high mortality disease" in any circumstance and that the U.N. health agency was still focused on trying to get sick people isolated and provide treatment as early as possible.
Previously, WHO had said the death rate was around 50 per cent.
THIS IS A BREAKING NEWS UPDATE. Check back soon for further information. AP's earlier story is below.
A World Health Organization official says there could be up to 10,000 new cases of Ebola per week within two months.
WHO assistant director-general Dr. Bruce Aylward says if the response to the Ebola crisis isn't stepped up within 60 days, "a lot more people will die" and there will be a huge need on the ground to deal with the spiraling numbers of cases. He said WHO estimated there could up to 10,000 cases per week in two months.
Aylward said for the last four weeks, there have been about 1,000 new cases per week, though that figure includes suspected, confirmed and probable cases. He said WHO is aiming to have 70 per cent of cases isolated within two months to reverse the outbreak.
WHO increased its Ebola death toll tally to 4,447, nearly all of them in West Africa, and the group said the number of probable and suspected cases was 8,914.
Sierra Leone, Guinea and Liberia have been hardest hit. Aylward said WHO was very concerned about the continued spread of Ebola in the three countries' capital cities —Freetown, Conakry and Monrovia. He noted that while certain areas were seeing cases decline, "that doesn't mean they will get to zero."
He said the agency was still focused on trying to treat Ebola patients, despite the huge demands on the broken health systems in West Africa.
"It would be horrifically unethical to say that we're just going to isolate people," he said, noting that new strategies like handing out protective equipment to families and setting up very basic clinics — without much treatment — was a priority.