The Ebola virus may have the "upper hand" in an outbreak that has killed more than 1,400 people in West Africa but experts can stop its spread, a top US health official said as he visited the hardest-hit countries.

Dr Tom Frieden, the director of the US Centre for Disease Control and Prevention, was in Liberia on Tuesday, and later plans to stop in Sierra Leone and Guinea.

Nigeria also has recorded cases, but officials there are optimistic that the spread can be controlled.

"Lots of hard work is happening," Frieden told a meeting attended by president Ellen Johnson Sirleaf on Monday. "But the virus still has the upper hand."

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Frustration is mounting over the slow collection of dead bodies from areas of the Liberian capital, Monrovia.

One group of residents attached plastic ties to the wrists and ankles of one suspected Ebola victim and dragged his corpse to a busy street.

Authorities have decreed that all Ebola victims must be collected by government health workers and cremated, as contact with bodies can transmit the virus. 

Liberian officials already have sealed off an entire slum area in the capital.

In Nigeria, two more Ebola patients were declared to have survived the disease and were discharged from hospital, said the health minister Onyebuchi Chukwu on Tuesday.

Five people have died from the disease in Nigeria, while seven have recovered. One person remains in the hospital in an isolation ward, said Chukwu.

A separate Ebola outbreak emerged over the weekend in Congo, though experts say it is not related to the West African epidemic.

Doctors Without Borders, which is running many of the treatment centers in the West Africa outbreak, said it was also sending experts and supplies to Equateur, a northwestern province of Congo.

But the medical charity has already warned that its resources already were stretched.

"In normal times, we're able to mobilise teams specialising in hemorrhagic fevers, but currently we are facing an enormous epidemic in West Africa, limiting our capacity to respond to the outbreak in Equateur province," said Jeroen Beijnberger, the group's medical coordinator in Congo.

Source: Agencies