Monrovia, Liberia: The United States and Britain will send medical equipment and military personnel to help contain West Africa's Ebola outbreak, as the World Health Organisation 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 2000 people. An "exponential increase" in new cases is expected in the hardest-hit countries in coming weeks, the UN 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," 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 3500 people have been infected, nearly half of them in Liberia. The outbreak has taken a particularly heavy toll on health workers. The World Health Organisation announced on Monday that one of its doctors working in Sierra Leone has been infected with Ebola.