The U.S. Peace Corps said on Wednesday it was pulling all 340 volunteers from Liberia, Sierra Leone and Guinea because of the spreading Ebola virus that has killed 672 people in the three countries since February.
A Peace Corps spokesperson said two volunteers were isolated and under observation after being exposed to a person who later died of Ebola.
"These volunteers are not symptomatic and are currently isolated and under observation," the spokesperson said in a statement.
The Peace Corps, citing privacy concerns, declined to say where the two volunteers had come into contact with the Ebola victim.
The two volunteers would return to the United States once they were cleared to travel, the Peace Corps spokesperson added.
It is the worst outbreak on record of the deadly virus, according to the World Health Organization. The virus is thought to stem from wild animals like forest bats and is transmitted between humans by touching victims or through bodily fluids.
Earlier, the Peace Corps said it was "temporarily removing its volunteers from Liberia, Sierra Leone and Guinea due to the increasing spread of the Ebola virus."
The Peace Corps currently has 102 volunteers in Guinea, 108 in Liberia and 130 in Sierra Leone working in the areas of education, health and agriculture.
The State Department has confirmed that one U.S. citizen died from Ebola in Nigeria after being infected in Liberia. Two other American aid workers infected with Ebola - Dr. Kent Brantly and missionary Nancy Writebol - are in serious condition, but have shown slight improvement.
They were part of a team in Liberia from North Carolina-based Christian relief groups Samaritan's Purse and SIM.
Reporting by Lesley Wroughton; Editing by Sandra Maler, Peter Cooney and Diane Craft