A Samaritan's Purse team member hands out pamphlets to educate the public on the Ebola virus in Monrovia, Liberia in this undated handout photo courtesy of Samaritan's Purse. [Photo/Agencies]

The US Peace Corps said on Wednesday it was temporarily withdrawing 340 volunteers from Liberia, Sierra Leone and Guinea and that two of its volunteers had been isolated and were under observation after coming in contact with a person who later died of the Ebola virus.

The Peace Corp has 102 volunteers in Guinea, 108 in Liberia and 130 in Sierra Leone working in education, health and agriculture.

The State Department has confirmed that one US 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 they have shown slight improvement. They were part of a team in Liberia from North Carolina-based Christian relief groups Samaritan's Purse and SIM.

"When these measures are instituted, only healthcare workers will be permitted to move in and out of those areas. Food and other medical support will be provided to those communities and affected individuals," she said, adding that all markets in border areas are to be closed.

White House spokesman Eric Schultz told reporters that President Barack Obama had been briefed on Tuesday by his homeland security adviser, Lisa Monaco, and that the White House was monitoring the deadly outbreak.

"The CDC (US Centers for Disease Control and Prevention) has said this is not a risk to the United States at this time," Schultz told reporters traveling with the president back to Washington from Kansas City, Missouri. He said the US government had increased assistance to countries battling Ebola.

Schultz said the White House would proceed with a planned US-Africa Leaders Summit in Washington Aug. 4-6 that about 50 Africa leaders are expected to attend to discuss trade and investment between the United States and Africa.

Liberia's President Surleaf said she would not be attending the summit but that Vice President Joseph Nyuma Boakai and a few cabinet ministers "whose presence are absolutely necessary" would attend.

"We have no plans to change any elements of the US-Africa Leaders Summit as we believe all air travel continues to be safe," Schultz said.

Last week, 40-year-old Liberian-American Patrick Sawyer, a consultant for the Liberian finance ministry, died from Ebola in Nigeria after having traveled from Liberia. Authorities in Nigeria, as well as Ghana and Togo, through which he passed en route to Lagos, are trying to trace passengers who were on the same plane as he was.

On Wednesday, Britain held a top-level government meeting to discuss the spread of Ebola in West Africa, saying the outbreak was a threat it needed to respond to.