Mali is on alert over the deadly Ebola virus after three suspected cases were reported near the border with Guinea, where 86 people have died.
A BBC correspondent says there are tight controls on people entering the capital, Bamako, from the border area.
He says thermal-imaging cameras are screening passengers at the airport in case they have a fever.
The virus, which is spread by close contact and kills 25%- 90% of its victims, has already spread to Liberia.
Meanwhile, an Air France plane which landed in Paris from Guinea was quarantined for two hours on Friday morning after the crew suspected a passenger was infected with Ebola.
"The test turned out negative," a spokesman for the airline said.
Six people have died in Liberia, out of 12 suspected cases, according to the local health authorities.
Sierra Leone has also reported suspected cases, while Senegal has closed its normally busy border with Guinea.
The BBC's Alou Diawara in Bamako says the three people feared to have Ebola have been moved to isolation wards on the edge of the city.
Samples have been sent to the US for testing and the results are expected in a few days.
Mali's government has advised its nationals against all non-essential travel to areas affected by Ebola.
WHO spokesperson Tarik Jasarevic in Conakry told the BBC the reports of cases in Mali were a "concern".
"Everyone should be vigilant and aware of what is going on. But we need to wait for the results to confirm if it is Ebola," he said.
The virus was first spotted in Guinea's remote south-eastern region of Nzerekore, where most of the deaths have been recorded.
But it was not confirmed as Ebola for six weeks.
It has now spread to Guinea's capital, Conakry, where five deaths have been recorded out of 12 suspected cases.
Saudi Arabia suspended visas for Muslim pilgrims from Guinea and Liberia on Tuesday, in a sign of the growing unease about the outbreak.
This is the first known outbreak in Guinea - most recent cases have been thousands of miles away in the Democratic Republic of Congo and Uganda.
There is no known cure or vaccine for Ebola.
The tropical virus leads to haemorrhagic fever, causing muscle pain, weakness, vomiting, diarrhoea and, in severe cases, organ failure and unstoppable bleeding.