WASHINGTON (AFP) - An American doctor who was recently infected with the Ebola virus in Liberia arrived in the United States on Friday for treatment.

Dr Rick Sacra was taken to the Nebraska Medical Centre in Omaha in the early morning, facility spokesman Jenny Nowatzke told AFP. "He is in a containment unit right now, being evaluated by our doctors," she said.

Local broadcaster KETV tweeted that Dr Sacra landed at the Offutt Air Force Base and transported to the center in an ambulance escorted by "numerous law enforcement vehicles".

Dr Sacra is the third American health worker to be infected with Ebola in the largest outbreak in history currently sweeping West Africa. Dr Kent Brantly and aid worker Nancy Writebol have recovered from their illnesses. They were flown back to the United States but treated at a different facility - Emory University Hospital in Atlanta, Georgia.

The virus has killed nearly 2,000 people in Guinea, Sierra Leone, Liberia and Nigeria since the beginning of the year, according to the World Health Organization.

Dr Sacra, 51, volunteered to go to Liberia for the Christian aid group SIM USA when Ms Writebol and Dr Brantly tested positive.

"Rick was receiving excellent care from our SIM/ELWA staff in Liberia at our Ebola 2 Care Center," Dr Bruce Johnson, president of SIM USA, said on Thursday.

"They all love and admire him deeply. However, the Nebraska Medical Center provides advanced monitoring equipment and wider availability of treatment options."

The Ebola virus has killed nearly 2,000 people in Guinea, Sierra Leone, Liberia and Nigeria since the beginning of the year, according to the World Health Organisation.