West Africa's Ebola epidemic constitutes an international health emergency and the virus, which has killed nearly 1,000 people, could continue spreading for months, the World Health Organization (WHO) said on Friday.

"The outbreak is moving faster than we can control it," the WHO's director-general Margaret Chan told reporters on a telephone briefing from the WHO's Geneva headquarters.

The UN agency's declaration, which follows criticism that it has done too little to fight the disease, is aimed at raising the level of vigilance about the virus which has hit hardest in Guinea, Liberia and Sierra Leone.

The agency said all states with Ebola transmission should declare a national emergency in the face of an outbreak it deemed "particularly serious" but there should be no general ban on international travel or trade.

"The declaration ... will galvanise the attention of leaders of all countries at the top level. It cannot be done by the ministries of health alone," Chan said.

The WHO has been accused of failing to respond fast enough to the outbreak, which it said on May 18 could be declared over by May 22. It has since become more conservative in its predictions, said head of health security, Keiji Fukuda.

"At that point we thought that it was likely that it would come under control based on our experience. This outbreak has developed in ways we have not seen before," Fukuda told reporters.

"The likelihood is that things will get worse before they get better," he said, adding that the WHO is prepared for an outbreak that persists at a high level for months.

Medical charity Medecins Sans Frontieres (MSF) said the declaration showed WHO's seriousness in tackling the outbreak but added that statements should be translated into action.

"For weeks, MSF has been repeating that a massive medical, epidemiological and public health response is desperately needed to saves lives," said Bart Janssens, MSF Director of Operations.

RESTRICTIONS

Ebola has no proven cure and there is no vaccine to prevent infection, so the best treatment is focussed on alleviating symptoms such as fever, vomiting and diarrhoea.

Its spread could be stopped with the right steps and measures to deal with infected people, Fukuda said, but it was important that anyone known to have Ebola should be immediately isolated and treated in isolation for 30 days.

The European Union said on Friday it is increasing by an additional 8 million euros ($10.7 million) its efforts to contain Ebola and governments in the region have taken increasingly tough measures in a bid to thwart the disease.

The army in Sierra Leone on Thursday blockaded rural areas hit by Ebola while neighbouring Liberia declared a state of emergency. But some local people said the restrictions, while necessary, risked increasing their economic hardship.

In one example, about 30 military officers armed with AK-47s guarded a checkpoint blocking a line of trucks laden with goods from travelling from Montserrado County to the rest of Liberia.

One of the drivers, Sackie Sumo, said the closed road prevented him transporting his truckload of logs, which in turn meant he would not be paid.

"I feel bad. I need to get money to my family," he told Reuters.

Market seller Musa Kweh whose shared taxi had been stopped at the same checkpoint, also said she was unsure how she would generate income from her goods now that the market in Monrovia she was heading to was closed.

In an attempt to make some money from the potatoes and other goods, she spread them on the ground at the checkpoint to sell to passersby.

FRESH DEATH TOLL

The latest WHO figures on Friday showed the worsening toll. Some 1,779 people have been infected and 961 people have died in the most severe outbreak in the 40 years since it was first identified in humans.

This was partly because of weaknesses in the countries affected, where health systems are fragile and lacking in resources. The effort to contain the disease is also undermined by inexperience and misperceptions of the threat, the WHO said.

Although most cases of Ebola are in the remote area where Guinea borders Sierra Leone and Liberia, alarm over the spread of the disease increased last month when a US citizen died in Nigeria after travelling there by plane from Liberia.

The US State Department has ordered the departure of eligible family members from its embassy in the Liberian capital Monrovia in the light of the disease and said it was acting "out of an abundance of caution".

Concerns have spread to other countries. Ugandan health authorities on Friday said an Ebola suspect had tested negative, while a hospital in Benin's capital is treating a Nigerian man suspected of having contracted the disease.

After an experimental drug was administered to two US charity workers who were infected in Liberia, Ebola specialists have urged the WHO to offer such drugs to Africans. The UN agency has asked medical ethics experts to explore this option next week. - Reuters