The deadly Ebola outbreak in Guinea, West Africa, remains in a "limited geographic area", the World Health Organization has said.
WHO spokesman Gregory Hartl said it was neither an epidemic, nor unprecedented.
But medical charity Medecins Sans Frontieres (MSF) has said its spread makes it very difficult to control.
The WHO says 83 people in Guinea have died in suspected cases of Ebola, which is spread by close contact and kills between 25% and 90% of its victims.
It has now spread to neighbouring Liberia, as well as Guinea's capital, Conakry, which has a population of two million people.
Liberia has recorded a total of seven suspected and confirmed cases, including four deaths.
Outbreaks of Ebola occur primarily in remote villages in Central and West Africa, near tropical rainforests, the WHO says.
"We need to be very careful about how we characterise something which is up to now an outbreak with sporadic cases," Mr Hartl told reporters in Geneva, Switzerland.
The WHO says the epidemiology of this outbreak is the same as previous outbreaks and remains localised, the BBC's Imogen Foulkes reports from Geneva.
The organisation adds that cases in Conakry and Liberia can be traced to the south-east of Guinea where the outbreak began.
On Monday, MSF described the outbreak as "unprecedented".
"We are facing an epidemic of a magnitude never before seen in terms of the distribution of cases," said Mariano Lugli, a co-ordinator in Guinea for the medical charity.
"This geographical spread is worrisome because it will greatly complicate the tasks of the organisations working to control the epidemic."
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.
Guinea has so far confirmed 122 cases of Ebola since January.
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.
Sierra Leone has also reported five suspected cases, none of which have yet been confirmed, while Senegal, which also borders Guinea, has closed its land border.
Saudi Arabia suspended visas for Muslim pilgrims from Guinea and Liberia on Tuesday, in a sign of the growing unease about the outbreak
The "preventive" measure came at the request of the Saudi health ministry "due to the danger of the disease and its highly contagious" nature, state news agency SPA reported.
The tropical virus leads to haemorrhagic fever, causing muscle pain, weakness, vomiting, diarrhoea and, in severe cases, organ failure and unstoppable bleeding.