The body of a dead Liberian man has tested positive for Ebola – the country's first reported case since it was declared free of the disease.
Deputy health minister Tolbert Nyenswah said tests confirmed that the 17-year-old man, from a town near the main airport, had died of the disease.
Officials are investigating how he contracted Ebola, Mr Nyenswah said.
Liberia was declared free of Ebola six weeks ago, following the deadliest outbreak in the disease's history.
More than 11,000 people have died of the disease since December 2013, the vast majority of them in Liberia, Guinea and Sierra Leone.
The countries had largely curbed the spread of the disease – but the number of new cases has risen recently, with the start of the rainy season in West Africa.
The news that a 17-year-old man has died of Ebola in Liberia is deeply troubling. The country was thought to be free of the deadly virus – no cases had been reported for the past seven weeks, until now.
Officials are urging people not to panic and instead "go about their business as normal". They say they have the situation in hand – the teenager's body was buried safely and surveillance has been stepped up.
But it is not clear how the young man caught the virus and who he may have been in contact with before he died. Liberians must remain vigilant if they are to banish Ebola for good.
Mr Nyenswah told the BBC's Jonathan Paye-Layleh in Monrovia that the authorities were dealing with the situation effectively and there was no need for the public to panic.
"We have said over and over again that there was possibility that there could be a resurgence of the virus in Liberia," he said. "But our surveillance team, our capacity is very strong.
"The only complication is that the person died before we tested the body as part of our surveillance system."
The dead man lived in Nedowein, a town 30 miles (48km) from the capital, near the country's international airport – but far from the borders with Guinea or Sierra Leone.
Mr Nyenswah said the authorities were investigating whether the dead man had contracted the disease as a result of travel.
He added that the man's body had been buried safely, in accordance with guidelines to check the spread of Ebola.