West Africa's raging epidemic of Ebola virus is an "extraordinary event" and now constitutes an international health risk, the World Health Organisation (WHO) said on Friday.

The Geneva-based United Nations health agency said the possible consequences of further international spread of the outbreak, which has killed almost 1,000 people in four West African countries, are "particularly serious" in view of the virulence of the virus.

"A coordinated international response is deemed essential to stop and reverse the international spread of Ebola," the WHO said in a statement after a two-day meeting of its emergency committee on Ebola.  - Reuters