WASHINGTON, Dec. 11 -- A U.S. nurse exposed to the Ebola virus while volunteering in an Ebola treatment unit in Sierra Leone has been admitted to the hospital of the National Institutes of Health (NIH) near Washington D.C., the NIH said Thursday.

The U.S. medical research agency said the patient arrived at the NIH Clinical Center Thursday afternoon "for observation and to enroll in a clinical protocol."

The patient was transferred from an overseas location via a private charter medevac in isolation, it said in a statement.

"Out of an abundance of caution, the patient has been admitted to the NIH Clinical Center's special clinical studies unit that is specifically designed to provide high-level isolation capabilities and is staffed by infectious diseases and critical care specialists," the statement said.

No additional details were released about the patient.

The NIH facility is one of four biocontainment units in the United States equipped to handle Ebola. It has successfully treated one of the 10 Ebola patients who received treatment in U.S. hospitals.