On Friday, WHO raised the death toll to at least 4,033 from 8,399 probable, suspected and confirmed Ebola cases

(Adds details throughout)

By Michelle Nichols

UNITED NATIONS, Oct 10 (Reuters) - A $1 billion United Nations appeal to fight Ebola has only been 25 percent funded and senior U.N. officials warned on Friday that no country was safe as the world faced a crisis with staggering potential.

"It is the most extraordinary challenge that the world could possibly face. You sometimes see films about this sort of thing and you imagine how could such a thing happen. This is more extreme than any film I have ever seen," said Dr. David Nabarro, who is heading the U.N. response to the Ebola epidemic.

Nabarro has said a "20-fold increase" in the global response is needed compared to efforts at the end of August. The United Nations has established a special mission, known as UNMEER, to coordinate efforts to stop the spread of Ebola.

The current outbreak of the hemorrhagic fever, which is the worst on record, was identified in March in a remote part of Guinea and has spread to West African countries Sierra Leone, Liberia, Nigeria and Senegal. Cases have also been reported in Spain and the United States.

The World Health Organization, the United Nations public health arm, has said an Ebola outbreak in Democratic Republic of Congo is unrelated to the one in West Africa.

On Friday, WHO raised the death toll to at least 4,033 from 8,399 probable, suspected and confirmed Ebola cases.

Nabarro told a special briefing of the 193-member U.N. General Assembly that the disease was spreading so rapidly the number of cases was likely doubling every three or four weeks.

Deputy U.N. Secretary-General Jan Eliasson appealed for more money and resources, including numerous healthcare personnel.

"Of the $1 billion sought by U.N. agencies under (the Office for the Coordination of Humanitarian Affairs) consolidated appeal only one quarter has been funded," Eliasson said.

U.S. Ambassador to the United Nations, Samantha Power, praised Cuba and East Timor for "punching far above their weight" with their contributions to the global Ebola response and appealed for assistance from more countries.

"According to the U.N.'s financial tracking service, only 24 countries have pledged $1 million or more to the efforts, 24 countries," Power told the General Assembly. "We have a responsibility to come together to meet this challenge."

East Timor has pledged $2 million to fight Ebola, while Cuba is sending hundreds of doctors and nurses to West Africa.

Power said the United States has so far given $156 million, deployed 100 disease experts and pledged to send some 4,000 military personnel to oversee construction of 17 treatment units in the region and establish a healthcare training hub.

Anthony Banbury, head of the U.N. Ebola mission in West Africa, said part of the challenge in combatting Ebola was changing behavior.

"The human response is to care, to empathize, to pay respect to the departed. With Ebola this type of response can be fatal," Banbury told the General Assembly by video link. "As long as there's one case of Ebola in any one of these countries, no country is safe from the dangers posed by this deadly virus."

(Reporting by Michelle Nichols; Editing by Toni Reinhold)

Our Standards: The Thomson Reuters Trust Principles.