The city of Mbandaka, which has one confirmed Ebola case, is an hour's flight from the capital, Kinshasa, and is located on the Congo River, a busy travel corridor.
Congo's latest Ebola outbreak now has 14 confirmed cases as health officials rush to contain the often deadly virus in a city of more than 1 million. The other was in Bikoro, the rural area where the outbreak was announced last week.
Forty-four cases have been reported in the outbreak so far, including three confirmed, 20 probable and 21 suspected, according to the WHO's tally. No details were given on the death's links to the newly confirmed case.
Previously, confirmed cases had been limited to a remote area more than 100 miles south of Mbandaka, in the rain forest of Congo's Equateur province.
Amid fears of the outbreak spreading to neighboring countries, the United Nations migration agency said Friday it would support the deployment of Congolese health teams to 16 entry points along the nearby border with the Republic of Congo for infection control and prevention. The WHO said it is deploying about 30 more experts to the city.
WHO-partner, MSF, has also deployed its teams and is working with United Nations agencies to strengthen health capacity to treat Ebola patients.
"This is a concerning development, but we now have better tools than ever before to combat Ebola", Tedros Adhanom Ghebreyesus, WHO director-general, said of the new urban case.More news: Iran, Syria, energy: What's in store for Putin-Merkel summit in Sochi
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Ebola is one of the world's most notorious diseases, being both highly infectious and extremely lethal.
Micaela Serafini, a medical director for the worldwide charity Medecins Sans Frontières (MSF) who is helping coordinate the response to the Congo outbreak, said its teams are planning for at least 45 minutes of discussion and information-sharing with each person, with a translator present, before signed consent would be obtained.
It also raised the regional risk to "high" from "moderate", but kept its assessment of the global risk at "low". The virus is transmitted to human through contact with wild animals and can then be passed from person to person.
The UN agency has been working with the Ministry of Health and Doctors Without Borders to conduct the ring fence vaccinations across the affected areas - where contacts of those infected, followed by contacts of those contacts, would all be vaccinated. The WHO has sent 4,000 doses to Congo and said it will dispatch thousands more as needed in the coming days.
Eleven people were treated for Ebola in the United States in 2014, two of whom died, according to the Center for Disease Control and Prevention.
Ebola is endemic in Congo, and this is the ninth outbreak of the disease there since the 1970s.
Ebola is lethal and highly contagious, which makes it hard to contain - especially in urban environments where people are mobile and come into more contact with others.