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.
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.
Ebola has been eradicated in Liberia, according to the World Health Organisation.
The West African nation has now gone 42 days without a new case - twice as long as its incubation period. More than 4,700 people died from the deadly virus over the last year.
Tolbert Nyswah, Liberia's deputy health minister, said that the news was "worth celebrating", but that vigilance was still needed while neighbouring countries Guinea and Sierra Leone still suffer.
A total of 11,005 people have died from Ebola in the three West African neighbours since the outbreak began in December 2013, according to the WHO.
Liberia was recording hundreds of new cases a week at the peak of the outbreak between August and October, causing international alarm.
Liberia has been declared free from Ebola on Saturday after 42 days without a new case, according to the medical charity Medecins Sans Frontieres (MSF), Reuters reports.
However MSF urged continued vigilance until the worst-ever recorded outbreak of the virus is extinguished in neighbouring Guinea and Sierra Leone.
MSF's head of mission in Liberia, Mariateresa Cacciapuoti, said: "We can't take our foot off the gas until all three countries record 42 days with no cases."
She urged Liberia to step up cross-border surveillance to prevent Ebola slipping back into the country.
A total of 11,005 people have died from Ebola in Liberia, neighbouring Guinea and Sierra Leone since the outbreak began in December 2013, according to the World Health Organisation (WHO).
Nearly half of those deaths have been in Liberia, where the outbreak peaked between August and October, with hundreds of cases a week.
A woman who was Liberia's last known patient with Ebola has died, according to a senior health official in the country.
President Obama is expected to issue an executive order to send US National Guard forces to Liberia to assist in the fight against Ebola, sources have told NBC News.
According to sources, no decision has been made, but the initial deployment would include eight guard and reserve engineers and logistics specialists to assist in the construction of seventeen 100-bed treatment centers for Ebola patients.
An executive would help cut through the usual official red tape and delays so that guard and reserve forces could be ordered to deploy to west Africa on a moment's notice.
While the initial force may be small in number the order would give the President the option to send further forces.
Oxfam has called for a greater focus on the prevention of new Ebola cases in West Africa in addition to managing existing cases and fatalities.
The charity says that many new Ebola cases are due to a "lack of access to basic washing facilities or because of their lack of knowledge about how the disease is spread".
It plans to triple its programmes in Sierra Leone and Liberia to provide water and hygiene and sanitation supplies, as well as public awareness campaigns.
An international medical official with the United Nations mission in Liberia tests positive for Ebola, according to Reuters citing the UN.
The official, who has not been identified, is the second member of the mission to contract the deadly disease. The first died last month.
An American cameraman working for NBC News in Liberia has tested positive for Ebola, the US network said.
The 33-year-old freelancer was on assignment in the country's capital of Monrovia covering the Ebola outbreak and will be flown back to the US for treatment.
NBC said the journalist, whose name has been withheld, is the fourth American to have contracted Ebola in Liberia.