Liberia has confirmed three new cases of Ebola and warned of possible new infections, raising fears hidden pockets of the disease remain in the country nearly two months after it was declared Ebola-free.

More than 11,200 people have died since last year in the worst Ebola outbreak on record, nearly all of them in the three neighbouring countries of Liberia, Sierra Leone and Guinea.

Liberia was declared Ebola-free on May 9 and, until now, had been viewed as a rare success story.

But the confirmation on Tuesday of an Ebola case in a rural area of Margibi County, about 50 kilometres from the capital Monrovia, raised fears of a resurgence of the disease.

The World Health Organisation (WHO) said Liberian authorities were monitoring more than 100 people thought to have come into contact with Abraham Memaigar, who died from the disease on Sunday.

The 17-year-old, initially misdiagnosed with malaria, was buried the same day but tests on his body later confirmed his infection.

A neighbour later also tested positive.

"We have, as of yesterday, three confirmed cases," deputy health minister Tolbert Nyenswah said on Thursday.

"One expired, who was the 17-year-old boy ... The two live cases are 24 years old and 27 years old. They are stable."

Liberian officials and the WHO said the teenager was not believed to have travelled to Sierra Leone or Guinea, with Margibi County far from the epidemic's remaining hotspots.

In past outbreaks, humans have been infected by eating monkey flesh and some residents of Mr Memaigar's village said that those showing symptoms of Ebola had recently eaten a dog, a common practice in Liberia.

"This might mean that there is a reservoir of Ebola in animals that we have not been paying attention to," said Dr Philip Ireland, from the John F Kennedy Medical Centre in Monrovia.

Dr Ireland, who is also an Ebola survivor, said: "It could pop up anywhere".

Cause of transmission unknown

In the village of Nedowein, Mr Memaigar's mud-brick home was under quarantine on Wednesday.

Health officials wearing rubber boots and gloves went house-to-house talking to residents confined to their homes.

"At present we have four people of high risk that have been taken to ... Monrovia. They are all from the community," said John Sumo, a member of the incident management team.

An internal Liberian health report showed that Mr Memaigar had attended school, visited a local clinic and travelled to his father's house in a nearby village in the week before he died.

Ebola, spread through bodily fluids, is most contagious in the late stages when victims can suffer bleeding from the eyes and ears as well as vomiting and diarrhoea.

The disease can remain present in semen long after a patient is cured.

It is also possible that the new infections resulted from a previously unidentified pocket of the disease.

Ebola is now believed to have been present in an area straddling the three countries long before the current outbreak was identified.

"It is likely that we'll find additional cases ... and if there are others, it would still be a cluster, just as there have been clusters for 40 years," said Dr Bernice Dahn, chief medical officer at Liberia's ministry of health.

Liberia helped to control the epidemic with the help of United States military assistance and hundreds of millions of dollars in aid.

However, most of those troops have now left the country however.

"It is like being kicked in the gut but at least we knew it might be coming," said Sheldon Yett, the representative for the United Nations children's agency UNICEF in Liberia.

"People have gotten into gear. There's no panic," Mr Yett said.

Reuters