MONROVIA (AFP) - Liberia announced the return of Ebola on Tuesday following the death of a 17-year-old boy, dealing a worrying blow to the country's recovery three months after its last known case.

Deputy health minister Tolbert Nyensuah told AFP the teenager had tested positive and died in Nedowian, a village beside the international airport, about an hour's drive from the capital Monrovia.

"We are investigating to know the origin of this new case. We ask all Liberians and all other nationals living in Liberia to continue taking preventive measures," he had earlier told public radio.

The case comes with the country still reeling from a nightmarish outbreak which wrecked its health service and economy and left thousands dead, just as it was recovering from more than a decade of civil war.

"Liberia now has the capacity to contain the new case, but remains vulnerable until we reach zero Ebola cases throughout the region," UNMEER, the UN's Ebola emergency response organization, tweeted.

Liberia had diagnosed its last victim, the wife of a cured patient, on March 20 -- its only case in more than a month -- and the country was finally declared Ebola-free six weeks after the woman's March 28 burial.

Nyensuah said experts had traced and quarantined anyone who may have had contact with the latest victim, without giving numbers or any further details on the patient.

Liberia's neighbors Guinea and Sierra Leone are both still battling the outbreak, which has killed more than 11,200 people, but the coastal Margibi County where the teenager died is much nearer Monrovia than either border.

The death follows equally disappointing news from Sierra Leone, which reported last week that the capital Freetown has suffered a fresh outbreak of Ebola, three weeks after its last case.