Two new cases of Ebola have been recorded in Guinea this week, according to the World Health Organisation, ending two consecutive weeks in West Africa when no cases of the disease were reported.
The two new patients were not previously identified contacts being tracked by health authorities, suggesting that officials are still unable to monitor everyone exposed to Ebola.
WHO spokeswoman Dr Margaret Harris said the UN health agency had expected to see more cases despite the recent lull in the epidemic.
She added the cases were in areas where scientists knew Ebola was spreading.
In an update this week, the WHO said there was a "near-term risk of further cases among both registered and untraced contacts".
To date, Ebola has killed more than 11,000 people in West Africa.