The death of a nurse in Mali from Ebola prompted on Wednesday the quarantine of more than 90 people in the West African country's capital, as the World Health Organization said the disease had now claimed at least 5,160 lives.

The worst outbreak of the virus on record has ravaged the impoverished West African countries of Liberia, Sierra Leone and Guinea and led to a global watch for cases outside the region.

Mali must now trace other people who had contact with the 25-year-old nurse and three others infected, just as an initial group of people linked to its first case completed their 21-day quarantine on Tuesday. Ebola's maximum incubation period is 21 days.

The more than 90 quarantined in Bamako included about 20 United Nations peacekeepers being treated at the capital's Pasteur Clinic, where the nurse worked, officials said. Police locked down the clinic on Tuesday night.

In Sierra Leone, more than 400 health workers at one of its few Ebola treatment centres went on strike over unpaid risk allowances, officials said. Some returned later in the day.

Echoing that walkout were protests and strikes by nurses across the United States over what they characterized as insufficient protection for health workers dealing with potential Ebola patients. Two nurses, who treated a Liberian man who died of the disease at a Dallas hospital in October, contracted the virus but recovered.

California-based National Nurses United had expected about 100,000 nurses nationwide to participate in the protest, but officials from the union could not say how many people participated.

In Washington, the Obama administration tried to assure sceptical US senators that its efforts to combat Ebola were making progress and urged lawmakers to approve $6.2 billion in new emergency funds to contain the virus.

"We believe we have the right strategy in place, both at home and abroad," US Health and Human Services Secretary Sylvia Burwell told the Senate Appropriations Committee.

Separately, the general leading the Ebola fight said the US military force being sent to Liberia to build treatment facilities was expected to top out at about 3,000 troops in December, 1,000 less than initially approved.

Ebola has killed at least 5,160 people out of at least 14,098 infected since March, predominantly in Liberia, Sierra Leone and Guinea, the WHO said in its latest status report from Geneva.

However, in a rare piece of good news, the WHO said there were signs that the incidence of new cases was declining in Guinea and Liberia, although it reported steep increases in Sierra Leone.

In Bamako, the nurse died after treating a Guinea man who died with Ebola-like symptoms that were not initially recognised, the government said.

The man, a Muslim imam from the border town of Kouremale, was never tested for the virus. In a series of rites that may have exposed many mourners to infection, his highly contagious body was washed in a Bamako mosque and returned to Guinea for burial without precautions.

The WHO said there were now four confirmed and probable Ebola deaths in Mali, adding that one was a friend who had visited the imam in the hospital. The group did not immediately give details on the fourth case.

A doctor at the Pasteur Clinic, one of Bamako's leading medical centres and the default clinic for expatriates, was also suspected of having Ebola and was being monitored.

The U.N. peacekeepers, who were at the clinic for injuries sustained while serving in Mali's turbulent north, were quarantined as a precaution, the U.N. mission said, without specifying their nationalities.

The government said the nurse was confirmed with Ebola on Tuesday and died later that evening. All necessary steps to identify people who had contact with the nurse were taken, it said.

Liberia, hardest hit of all with 2,836 deaths out of 6,822 cases, was another focal point on Wednesday in the battle against Ebola.

US Army General Gary Volesky, who is heading up the US military Ebola effort in Liberia, told a Pentagon telephone briefing that fewer US troops were needed there than initially expected because the military had discovered greater-than-anticipated local capacity for building treatment centres.

In the capital, Monrovia, former British Prime Minister Tony Blair met with President Ellen Johnson Sirleaf on a tour of that country, Sierra Leone and Guinea. Blair said $2 billion would be needed over the next few years to build more resilient public services, provide basic infrastructure and create jobs in Liberia, according to a statement from Sirleaf's office.

Despite the epidemic, the United Nations is not seeing signs of deteriorating security in Liberia, and some public authorities are even showing strength after years of post-civil war rebuilding, U.N. peacekeeping chief Herve Ladsous said.

"There is some good news in the midst of this serious crisis," Ladsous told the Security Council in New York. – Reuters