* 635 infected, 399 dead from disease since Feb, WHO says
* Outbreak has potential to spread to more countries
* Governments and partners must step up response
ABIDJAN, June 26 (Reuters) - An Ebola outbreak that began in Guinea has turned into a cross-border crisis that could spread to more countries, the World Health Organisation said on Thursday, calling for drastic action to halt the deadly epidemic.
Despite efforts by national health authorities and international aid organisations to contain its spread, the WHO has recorded 635 infections, including 399 deaths, in Guinea, Sierra Leone and Liberia since the outbreak began in February.
The crisis is already the deadliest outbreak since Ebola first emerged in central Africa in 1976, and the number of infections continues to rise.
"This is no longer a country specific outbreak but a sub-regional crisis that requires firm action by governments and partners," Luis Sambo, WHO Regional Director for Africa, said in a statement.
"WHO is gravely concerned by the on-going cross-border transmission into neighbouring countries as well as the potential for further international spread," he said.
In response to the worsening crisis, the WHO said it will convene a special meeting of health ministers from 11 countries in Accra, Ghana on July 2 and 3 to develop a comprehensive inter-country response plan.
Ebola - with a fatality rate of up to 90 percent, no vaccine and no known cure - has not previously occurred in the West Africa region. People there have become frightened of health facilities, blaming them for importing and spreading the virus.
The Ebola virus initially causes raging fever, headaches, muscle pain, conjunctivitis and weakness, before moving into more severe phases with vomiting, diarrhoea and internal and external haemorrhaging.
"There is an urgent need to intensify response efforts; to promote cross-border collaboration and information sharing of suspected cases and contacts...and to mobilise all sectors of the community," Sambo said. "This is the only way that the outbreak will be effectively addressed."
Medical charity Médecins Sans Frontières (MSF) said this week that a lack of understanding has meant people continue to prepare corpses and attend funerals of victims, leaving them vulnerable to a disease transmitted by touching victims or via bodily fluids.
MSF accused civil society groups, governments and religious authorities of failing to acknowledge the scale of the epidemic, resulting in few prominent figures promoting the fight against the disease.
(Reporting and writing by Joe Bavier; Editing by Raissa Kasolowsky)