Mali said it had identified its first possible cases of Ebola since the start of an outbreak in neighbouring Guinea, adding to fears that the deadly virus was spreading across West Africa.

Three people in Mali had been placed in quarantine and samples sent off to Atlanta in the United States for tests, the government said on state television late on Thursday.

"A high-speed intervention team has been created to follow the evolution of the situation on the ground," the statement said. It added that the health of the three suspected victims was showing signs of improvement.

More than 90 people have already died in Guinea and Liberia in what medical charity Medecins Sans Frontieres (MSF) has warned could turn into an unprecedented epidemic in an impoverished region with poor health services.

As news broke of the possible spread of the disease to Mali, an angry crowd attacked a MSF treatment centre in Guinea, accusing its staff of bringing the deadly disease to the town.

MSF spokesman Sam Taylor told Reuters that the attackers in Macenta, around 425km southeast of the capital Conakry, had accused staff of bringing the disease to the town.

"We have evacuated all our staff and closed the treatment centre," he said. "We have the full support of the local leaders and we're working with the authorities to try and resolve this problem as quickly as possible so we can start treating people again."

The latest outbreak originated in Guinea two months ago and has since spread to its neighbours Sierra Leone and Liberia.

Gambia has placed two people in quarantine although the health ministry since said the cases were negative.

Foreign mining companies have locked down operations and pulled out some international staff in mineral-rich Guinea.

French health authorities have also put doctors and hospitals on alert in case people travelling to and from former colonies in the region pick up the disease.

Many health systems in West Africa are poorly equipped to deal with an epidemic and aid workers have warned of the difficulty of fighting infections scattered across several locations and in densely populated areas such as Guinea's capital Conakry.

Guinea's health ministry said that two more suspected victims of the virus had died, bringing its death count to 86. Liberia also reported three new deaths among its suspected 14 cases, raising its death toll to seven.

"We need to fight to contain it. A medical team from MSF came today to help train some of our health workers," said Liberia's health minister Walter Gwenegale.

The disease, which has killed 1,500 since it was first recorded in 1976 in what is now Democratic Republic of Congo, causes vomiting, diarrhoea and external bleeding. It has a fatality rate of up to 90 percent.