The virus has now claimed at least 887 lives, the WHO reported, with 163 new cases and 61 deaths in just two days.
The latest update indicates the disease is picking up speed, with the number of new infections surging by 33% over the last three-day report ending July 27, and three new cases reported in Nigeria, the latest country to be hit by the disease.
Of the four cases there, three were classified as "probable," and one was "suspected," the WHO said.
At least one of the newly reported cases in Nigeria was said to be a doctor who was treating Liberian-American Patrick Sawyer, 40, who fell ill on a flight from Liberia to Lagos on July 20, and was immediately quarantined upon arrival.
Efforts to confirm that Sawyer indeed died of Ebola have been hampered by couriers who are unwilling to transport the biological samples for secondary testing, the WHO said last week.
Sawyer, who became the first reported Ebola death in Nigeria and who was scheduled to fly to the United States soon to visit his family, raised major concerns that the virus could continue to spread quickly from major population centers like Lagos, the continent's largest city and home to 21 million people.
Last week, the WHO called the apparent spread of the disease into a fourth territory a "significant development in the course of this outbreak."
"This outbreak is moving faster than our efforts to control it," Dr. Margaret Chan, director-general of the World Health Organization, told leaders of four West African countries gathered in Conakry, Guinea, last week. "If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives but also severe socioeconomic disruption and a high risk of spread to other countries."
In a press briefing Monday, White House spokesman Josh Earnest said the
In addition, Earnest said, authorities are screening travelers who are entering major U.S. airports from the affected countries and will quarantine them if necessary.
The CDC last week issued a travel advisory, warning travelers against non-essential travel to Guinea, Sierra Leone and Liberia, for fear that travelers might get exposed to Ebola if they needed medical care in a hospital overwhelmed by patients.