President Barack Obama has authorized the Pentagon to call up reserve and National Guard troops if they are needed to assist in the U.S. response to the Ebola outbreak in West Africa.
The United States has already committed to sending up to 4,000 military personnel to Ebola-stricken countries to provide logistics and help build treatment units to confront the rapidly spreading and deadly virus.
But amid rising criticism over the handling of the patients in the U.S., the White House resisted calls from Republican lawmakers that a travel ban be imposed on those wishing to fly to America from Liberia, Sierra Leone and Guinea — the countries that have been worst hit by the outbreak.
The vast majority of the near 4,500 deaths from Ebola occurred in the three impoverished nations.
In announcing the executive order permitting the deployment of National Guard troops, the White House said the additional personnel would not be providing direct health care aid in the countries.
The move comes one day after the president directed his staff to respond in a "much more aggressive way" to the threat posed by Ebola.
Meanwhile, the World Health Organization said Thursday that the Ebola death toll is likely to hit 4,500 this week. It has projected that there could be between 5,000 and 10,000 new cases a week in early December unless urgent action is taken.
"Ebola is a huge and urgent global problem that demands a huge and urgent global response," U.N. Secretary-General Ban Ki-moon said Thursday.
A trust fund launched by Ban in efforts to raise $1 billion in flexible funding for the fight against Ebola has only $100,000 in the bank, he acknowledged.
The money is crucial if the United Nations is to "get ahead of the curve and meet our target of reducing the rate of transmission by Dec. 1," Ban said, adding that to date, $20 million has been pledged.
Also on Thursday, federal health officials in the U.S. said they still don't know how two Dallas nurses caught Ebola from a patient.
The acknowledgment did little to tamper criticism from lawmakers, who have questioned whether the nation is prepared to stop the deadly virus from spreading in the U.S.
The revelation that one of the hospital nurses was cleared to fly on a commercial airline the day before she was diagnosed also raised alarm about the American response to the Ebola outbreak.
Nevertheless, Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said "despite these latest incidents, we remain confident that our public health and health care systems can prevent an Ebola outbreak here," in prepared testimony for the hearing on Capitol Hill.
On Wednesday, 29-year-old Amber Joy Vinson, the second Dallas nurse diagnosed with Ebola, was transported to Emory University Hospital in Atlanta. Emory and three other U.S. hospitals have specialized isolation units to care for Ebola with less risk of spread to health care workers.
Vinson was closely monitored after Nina Pham, another health care worker involved in Duncan's care, was diagnosed with Ebola last weekend. Texas Health officials said Wednesday that Pham was in good condition. It wasn't immediately clear why she's being moved.
Al Jazeera and wire services