The World Health Organization warned on Monday that many thousands of new infections are expected in Liberia in the coming weeks.
The current Ebola outbreak is the largest on record. It has spread from Guinea to Sierra Leone, Liberia, Nigeria and Senegal and killed more than 2,000 people. An "exponential increase" in new cases is expected in the hardest-hit countries in coming weeks, the U.N. health agency warned.
"As soon as a new Ebola treatment facility is opened, it immediately fills to overflowing with patients, pointing to a large but previously invisible caseload," the WHO said in a statement about the situation in Liberia. "Many thousands of new cases are expected in Liberia over the coming three weeks."
So far, more than 3,500 people have been infected, nearly half of them in Liberia. The outbreak has taken a particularly heavy toll on health workers. The WHO announced on Monday that one of its doctors working in Sierra Leone has been infected with Ebola.
In response to the spiraling disaster, U.S. President Barack Obama said on Sunday that the military would help to set up isolation units and provide security for public health workers responding to the outbreak.
In addition, Britain will open a 62-bed treatment center in Sierra Leone in the coming weeks. It will be operated by military engineers and medical staff with help from the charity Save the Children, Britain's Department for International Development said on Monday.
The clinic will also include a special section for treating health care workers, offering them high-quality, specialist care, the statement said.
Currently, there are about 570 beds in Ebola treatment centers in Guinea, Sierra Leone and Liberia, the hardest-hit countries, and the WHO says nearly 1,000 more are needed, the vast majority of those in Liberia.
Doctors Without Borders welcomed both the U.S. and British announcements, but warned even the latest surge in efforts may not be enough, saying the disease was moving "catastrophically through the population much faster than new facilities are being created."
U.N. Secretary-General Ban Ki-moon called several world leaders over the weekend, including the British prime minister and French president, to urge them to send more medical teams and money to fight the outbreak.
Officials have said flight bans and border closures — meant to stop the disease's spread — are slowing the flow of aid and protective gear for doctors and nurses to the region.
At an emergency African Union meeting on Monday, members agreed to open borders that have been closed and lift bans on flights to and from affected countries, according to Nkosazana Dlamini Zuma, chair of the AU's Commission. But it was unclear how quickly those promises would be kept.
Earlier, Senegal, which has shut its borders and blocked flights, said it was planning to open a "humanitarian corridor" to the affected countries.