The Ebola outbreak that has killed 78 people in Guinea is "unprecedented", a medical charity has said.
An official with Medecins Sans Frontieres (MSF) said the spread of the disease across the country made it very difficult to control.
The West African state is facing a battle to contain the outbreak after cases were reported in areas that are hundreds of kilometres apart.
Ebola is spread by close contact and kills between 25% and 90% of victims.
"We are facing an epidemic of a magnitude never before seen in terms of the distribution of cases," Mariano Lugli, a co-ordinator in Guinea for the aid group said.
"This geographical spread is worrisome because it will greatly complicate the tasks of the organisations working to control the epidemic," Mr Lugli added.
The outbreak of Ebola had centred around Guinea's remote south-eastern region of Nzerekore but it took the authorities six weeks to identify the disease.
It has now spread to neighbouring Liberia, as well as Guinea's capital, Conakry, which has a population of two million people.
Senegalese singer Youssou Ndour cancelled a concert in Conakry on Saturday because of the outbreak.
Although he had already travelled to the city, he told the BBC it would not be a good idea to bring hundreds or thousands of people together in an enclosed area.
Figures released overnight by Guinea's health ministry showed that there had been 78 deaths from 122 cases of suspected Ebola since January, up from 70.
Of these, there were 22 laboratory confirmed cases of Ebola, the ministry said.
Liberia has recorded a total of seven suspected and confirmed cases, including four deaths, the World Health Organization (WHO) said.
Liberia's Health Minister Walter Gwenigale on Monday warned people to stop having sex because the virus was spread via bodily fluids.
This was in addition to existing advice to stop shaking hands and kissing.
The BBC's Jonathan Paye-Layleh in Monrovia, the capital of Liberia, says residents are increasingly concerned and many supermarket workers are wearing gloves as a precaution.
The first two Liberians confirmed as dying from Ebola were sisters, one of whom had recently returned from Guinea.
Sierra Leone has also reported five suspected cases, none of which have been confirmed yet, while Senegal, another neighbour of Guinea's, has closed its land border.
Outbreaks of Ebola occur primarily in remote villages in Central and West Africa, near tropical rainforests, WHO says.