Ebola continues to spread in Sierra Leone, Liberia and Guinea, with a combined 44 new cases and 21 deaths between July 6 and 8, the World Health Organisation has said.

This brought the total in West Africa's first outbreak of the deadly disease to 888 cases, including 539 deaths since February. It is the largest and deadliest so far, the UN agency said.

"The epidemic trend in Liberia and Sierra Leone remains precarious with high numbers of new cases and deaths being reported," the WHO said on Friday.

Just one confirmed new case had been reported during the past week in Guinea.

The Economic Community of West African States set up an Ebola solidarity fund at a summit in the capital of Ghana on Thursday in a bid to back a regional approach to the epidemic. Nigeria committed $3.5m to affected states.

"We must do everything within our means and power to defeat this deadly disease. We must exercise vigilance and caution and avoid any panic or misinformation," Ghanaian President John Mahama, the group's chairman, said in a speech in Accra.

Ebola causes fever, vomiting, bleeding and diarrhoea and kills up to 90 percent of those infected. It is highly contagious and is transmitted through contact with blood and other fluids.

The WHO has flagged three main factors driving its spread: the burial of victims in accordance with tradition, the dense populations around the capital cities of Guinea and Liberia and the bustling cross-border trade across the region.