The United Nations said $600 million in supplies would be needed to fight West Africa's Ebola outbreak, as the death toll from the worst ever epidemic of the virus topped 1,900 and Guinea warned it had penetrated a new part of the country.

The pace of the infection has accelerated, and there were close to 400 deaths in the past week, officials said on Wednesday.

An experimental Ebola vaccine that Canada said it would give to the World Health Organization for use in Africa was as of Wednesday still in the lab that developed it as officials are puzzled over how to transport it, Reuters reports.

The U.S. Department of Health and Human Services said on Tuesday a federal contract worth up to $42.3 million would help accelerate testing of an experimental Ebola virus treatment being developed by privately held Mapp Biopharmaceutical Inc.

Dr. David Nabarro, senior U.N. Coordinator for Ebola, said the cost of getting the supplies needed by West Africa countries to control the crisis would amount to $600 million. That was higher than an estimate of $490 million by the WHO last week.

Dr. Margaret Chan, director-general of the World Health Organization (WHO) told a press conference in Washington, "This Ebola epidemic is the longest, the most severe and the most complex we've ever seen."

Chan said there were more than 3,500 cases across Guinea, Liberia and Sierra Leone.

The WHO warned last week that the Ebola epidemic in West Africa could infect more than 20,000 people and spread to 10 countries.