The head of the World Health Organisation has said the Ebola outbreak in West Africa is moving faster than efforts to control it.

Margaret Chan said governments may need to impose restrictions on population movements and public gatherings, and use police to guarantee the security of Ebola response teams.

The disease has killed 729 people in Guinea, Liberia, Nigeria and Sierra Leone, with the number of cases exceeding 1,330.

Ms Chan said the virus can be contained, but said the demands created by Ebola in West Africa outstrip the affected countries' capacity to respond.

She said: "If the situation continues to deteriorate, the consequences can be catastrophic in terms of lost lives but also severe socio-economic disruption and a high risk of spread to other countries."

Ms Chan described the outbreak as "by far the largest ever in the nearly four-decade history of this disease".

"It is taking place in areas with fluid population movements over porous borders, and it has demonstrated its ability to spread via air travel, contrary to what has been seen in past outbreaks.

"Cases are occurring in rural areas which are difficult to access, but also in densely populated capital cities."

The WHO has convened an emergency committee on 6-7 August to decide if Ebola constitutes a public health emergency of international concern and to recommend measures to tackle it.

Meanwhile, the leader of Guinea's Ebola task force has said that moves by Liberia and Sierra Leone to contain the disease may have the opposite effect.

Liberia has put in place several measures, including closing all schools and some government departments, as well as possibly quarantining affected communities.

Sierra Leone declared a state of emergency and called in troops to isolate Ebola victims.

"Currently, some measures taken by our neighbours could make the fight against Ebola even harder," said Aboubacar Sidiki Diakit before a meeting of heads of state from the three West African nations to coordinate a regional response.

"When children are not supervised, they can go anywhere and make the problem worse. It is part of what we will be talking about."

The outbreak of the virus, for which there is no known cure, began in the forests of eastern Guinea in February, but Sierra Leone now has the highest number of cases.

The haemorrhagic virus can kill up to 90% of those infected, though the fatality rate in this epidemic is about 60%.

In the final stages, its symptoms include external bleeding, internal bleeding, vomiting and diarrhoea - at which point Ebola becomes highly contagious.

The WHO said yesterday it would launch a €75m response plan.

The United States said it was providing material and technical support to the three countries and further assistance will be discussed next week.

The head of the US Centres for Disease Control and Prevention has also announced plans to send an extra 50 health experts to help efforts to control the epidemic.