09/02/2014 11:12 EDT | Updated 11/02/2014 05:59 EST

Ebola outbreak: 'We need action now,' says CDC director Tom Frieden

Despite tremendous efforts to fight the Ebola outbreak on the part of governments in West Africa, cases continue to increase rapidly, the director of the U.S. Centers for Disease Control and Prevention warned Tuesday.

Dr. Tom Frieden gave an update on the outbreak to reporters on Tuesday, one day after his return from the West African countries most affected by the outbreak: Guinea, Liberia and Sierra Leone. 

"We need action now to scale up response," Frieden said. "The world needs to respond."

The virus has killed around 1,550 people since the latest outbreak was detected in March.

In a speech to the United Nations on Tuesday, Dr. Joanne Liu, international president of Doctors Without Borders, denounced the lack of deployment of resources to address the outbreak, which the group says has overstretched ministries of health and private non-governmental organizations.

"Many countries possess biological threat response mechanisms. They can deploy trained civilian or military medical teams in a matter of days, in an organized fashion, and with a chain of command to assure high standards of safety and efficiency to support the affected countries."

Doctors Without Borders said any military assets and personnel deployed to the region should not be used for quarantine, containment, or crowd control measures.