A 15-year-old boy has died of Ebola in Liberia, which was previously declared free of the virus.
The boy's father and brother have also tested positive for the virus and have been taken to a treatment centre along with his mother and two other siblings.
Health officials have identified nearly 160 people who might be at risk of the disease, including 10 healthcare workers who came into direct contact with the boy.
The source of the virus is being investigated but it is the first death in Liberia since July.
Liberia has recorded more than 4,800 Ebola deaths and more than 10,600 cases since this year's outbreak.
It was first declared Ebola-free on May 9, but new cases emerged in June resulting in two deaths.
The World Health Organization declared the country Ebola-free again on September 3.
The World Health Organisation (WHO) failed to act quickly to contain the spread of the Ebola virus, a critical new report has said.Read the full story ›
A case of Ebola has been confirmed in a 10-year-old boy in Liberia - which was previously declared free of the disease.
The boy is currently being seen by medics at the treatment center on the outskirts of the capital Monrovia.
Liberia was first declared Ebola-free on May 9 - but there was a resurgence of the disease in late June infecting four people and two later died.
The country was again declared Ebola-free on September 3 by the World Health Organization.
Chief Medical Officer Dr. Francis Kateh told AP on Friday the boy, a resident of the eastern Paynesville district of Monrovia, was taken to the Ebola treatment unit late Thursday.
He confirmed the boy had Ebola.
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Nurse Pauline Cafferkey has made a "significant improvement" after becoming unwell with meningitis caused by the Ebola virus.
The 39-year-old from Glasgow has been receiving treatment in the Royal Free Hospital's high level isolation unit since October 9 and was at one point in a critical condition.
On Wednesday, the hospital's Dr Michael Jacobs revealed she had not been reinfected with Ebola, but that the virus had re-emerged to cause meningitis.
"I'm really pleased to tell you that in the last few days she has made a significant improvement," Dr Jacobs told a press conference.
He said Ms Cafferkey was still bed-bound but was talking freely and able to eat a little.
Dr Jacobs said staff were "delighted" with her progress but that she had a "long recovery ahead of her" and would remain in hospital for some time.
Nurse Pauline Cafferkey's condition "has improved to serious but stable" after being treated for Ebola for a second time, Royal Free Hospital has said.
The 39-year-old from Glasgow has been receiving treatment in the hospital's high level isolation unit since 9 October due to a late complication of her previous infection.
Nurse Pauline Cafferkey is likely to be suffering a reaction to the Ebola virus, according to a leading expert.
Professor John Oxford said a very small amount of the virus could be lingering in the nurse's body despite the treatment she originally received.
Prof England said: "Lots of viruses, even the more common ones that we get in England like mumps, measles or used to before the vaccine came in Rubella things like that, children would recover - acute phase - but then months later, maybe even a year later, they'd be seriously ill again.
"They wouldn't have the rash, wouldn't have the original disease as such, they'd have a reaction to that original disease, maybe because of their own immune reaction.
"Pauline is surviving because of her immune system but you can get an overreaction. That's possibly causing some of the symptoms now."
The return of the Ebola virus in nurse Pauline Cafferkey is "concerning", a virologist said.
Professor Andrew Easton, of Warwick University, said that although the virus had persisted in a patient before, it was unusual so long after the first diagnosis.
He said: 'We haven't seen it return after this long. It is concerning. There are lots of unknowns at this stage. It is very difficult to tell and I don't want to predict what the outcome may be.'
Ebola can occasionally persist for some months in certain tissues within survivors as it is retained by parts of the body where the immune system struggles to reach. These include the testes and the liquid in the back of the eye.
Prof Easton added that Ms Cafferkey's condition may have worsened as the virus pushes back from where it was contained - meaning she would go through the same stages of the virus as she had previously.
Nurse Pauline Cafferkey is the first recorded victim to suffer a relapse of Ebola in the world.
The 39-year-old is critically ill in the Royal Free hospital in London being treated for Ebola, not a complication from it.
It raises questions about the treatment she received back in January and how effective the treatment was.
ITV News Health Editor Rachel Younger reports: