A second person in Liberia has died from Ebola on July 15 in a resurgence of the deadly virus and the outbreak had spread to its capital city.
The sixth confirmed case since the virus re-emerged at the end of June was a healthcare worker in Monrovia, said chief medical officer Francis Karteh.
"Now we have four cases in (treatment). We have six confirmed cases in Liberia -- two are already dead," he said.
The latest cluster of infections emerged in a village near the international airport in the coastal county of Margibi, when a 17-year-old boy tested positive for Ebola after his death.
"Ebola is no longer confined to Margibi County. A case has been reported in Monrovia, but has been reported expired," Karteh said.
"The case was carried in a critical condition to the (Ebola treatment unit) and later died."
The man was being monitored as a known contact of one of the previous cases, but hid his illness from the authorities by taking medication to bring down his temperature, Karteh said.
He warned that efforts to contain the outbreak were being hampered by people not admitting they'd had contact with Ebola patients.
"We need to be open. We need to be honest to ourselves. It is through honesty that we can stop this disease... If you are to go to a general clinic with a fever you need to tell the healthcare worker that you are a contact," he said.
The world's worst Ebola outbreak has killed more than 11,250 people in west Africa, brought fragile health care systems to their knees, rolled back economic gains and sent investors fleeing.
The epidemic spread to Liberia from Guinea in March 2014, killing more than 4,800 Liberians before the World Health Organization (WHO) declared the country free of transmission on May 9 this year.
Tests on the 17-year-old showed the variant which killed him was genetically similar to the 2014 outbreak.
The WHO said this showed that the resurgence of the disease was unlikely to be due to the virus being re-introduced from Sierra Leone, which is also battling the outbreak, or Guinea.
New infections in Sierra Leone and Guinea have fallen dramatically, although the two countries are still reporting more than 20 new cases each week between them.