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The World Health Organisation and medical charity Medicins Sans Frontieres said on Friday (local time) the outbreak, which has killed 729 people in four West African countries, was out of control and more resources were urgently needed to deal with it.
WHO chief Margaret Chan told a meeting of the presidents of Guinea, Liberia and Sierra Leone - the countries worst affected - that the epidemic was outpacing efforts to contain it and warned of catastrophic consequences in lost lives and economic distruption if the situation were allowed to deteriorate.
"The presidents recognise the serious nature of the Ebola outbreak in their countries," Chan said after the meeting. "They are determined to take extraordinary measures to stop Ebola in their countries."
In a communique after their talks, the leaders agreed to deploy security forces to isolate the frontier regions where 70 percent of the 1,323 cases have been detected.
They banned the transportation of anyone showings signs of disease across borders, and pledged to introduce strict controls at international airports to prevent the virus spreading outside the region.
There was international alarm last week when a U.S. citizen died of Ebola in Nigeria - Africa's most populous country - after flying there from Liberia. Two people quarantined in Lagos after coming into contact with him were released on Friday after they tested negative for the disease.
The three leaders also agreed to step up efforts to protect local healthcare workers and encourage them to return to work.
With healthcare systems struggling to cope with the highly infectious disease, which requires rigorous precautions to stop it spreading, more than 60 medical workers have lost their lives, hampering efforts to tackle the outbreak.
Liberia has already put in place tough measures including closing all schools and some government departments. Sierra Leone on Wednesday declared a state of emergency and called in troops to isolate Ebola victims.
However, Friday's agreement marked a reversal by Guinea, which had previously resisted taking tough steps, saying the disease was under control there.
"Somewhat drastic measures will be taken," Guinea's Cooperation Minister Moustapha Koutoub Sano said. "These (border) prefectures and communities will be isolated."
The outbreak has prompted some international organisations to withdraw. The U.S. Peace Corps has said it was withdrawing 340 volunteers from Liberia, Sierra Leone and Guinea.
U.S. aid group Samaritans Purse said on Friday it would complete the evacuation of its 60 international staff from Liberia over the weekend. It said two American staff who contracted the disease in Liberia were in a serious condition and would be medically evacuated by early next week.
Charity WaterAid said on Friday it was suspending its operations in Liberia as well.
The WHO is launching a $100 million response plan and the United States is providing material and technical support to the three countries. Further assistance will be discussed at a U.S.-Africa summit in Washington next week.
Guinea President Alpha Conde told Reuters he would represent Africa in those Ebola talks. Sierra Leonean President Ernest Bai Koroma and Liberia's Ellen Johnson-Sirleaf announced this week they would remain at home to tackle the crisis.
Chan appealed on Friday to the wider world to provide more medical experts and funding. She pledged to take personal responsibility for coordinating international response efforts and mobilising the vast support needed to fight the virus, which can kill up to 90 percent of those infected.
The fatality rate in this epidemic is about 60 percent.
The WHO has convened an emergency committee on Aug. 6-7 to decide if the outbreak constitutes a public health emergency of international concern and to recommend measures to tackle it.
"The demands created by Ebola in West Africa outstrip your capacities to respond," Chan told the presidents.
Chan said cultural practices such as traditional burials and deep-seated beliefs were a significant cause of the spread and needed to change. In the final stages, its symptoms include external and internal bleeding, vomiting and diarrhoea - at which point Ebola becomes highly contagious.
On Friday, the government of southeastern Nigeria's Anambra state quarantined a mortuary containing the body of a Nigerian man who died in Liberia while tests were conducted to determine the caused of death.