The World Health Organization on Thursday called for "drastic action" to fight the deadliest Ebola outbreak on record, as it announced an 11-nation meeting to address the growing crisis.
As of Sunday, 635 cases of Ebola have been reported, including 399 deaths, making the outbreak the largest ever "in terms of the number of cases and deaths, as well as geographical spread," the UN agency said in a statement.
"As the number of deaths and cases of Ebola virus continues to rise in Guinea, Liberia and Sierra Leone, the World Health Organization is warning that drastic action is needed," WHO said.
Since west Africa's first-ever epidemic of the deadly haemorrhagic fever emerged in Guinea in January, WHO has sent in more than 150 experts to help tackle the crisis.
But despite the efforts of the WHO and others, there has been a "significant increase" in the number of cases and deaths reported each day for the past three weeks, it said.
The agency is now "gravely concerned (by) the on-going cross-border transmission into neighbouring countries as well as the potential for further international spread," said WHO's regional director for Africa, Dr. Luis Sambo.
"This is no longer a country specific outbreak but a sub-regional crisis that requires firm action by governments and partners," Sambo warned.
To address the growing crisis, the WHO said it would convene a meeting of the health ministers from 11 countries in Accra, Ghana on July 2 and 3 "to discuss the best way of tackling the crisis collectively as well as develop a comprehensive inter-country operational response plan."
In addition to the three countries affected so far, Ivory Coast, Democratic Republic of Congo, Gambia, Ghana, Guinea Bissau, Mali, Senegal and Uganda have also been invited to take part in the meeting.
A range of UN agencies and other aid organisations including Doctors Without Borders and the Red Cross will also participate, WHO said.
WHO has described the epidemic as one of the most challenging since the virus was first identified in 1976 in what is now the Democratic Republic of Congo.
That outbreak, until now the deadliest, killed 280 people, according to WHO figures.
Ebola is a tropical virus that can fell its victims within days, causing severe fever and muscle pain, weakness, vomiting and diarrhoea -- in some cases shutting down organs and causing unstoppable bleeding.
No medicine or vaccine exists for Ebola, which is named after a small river in the DRC.