WATCH: WHO warns over challenges of containing Ebola in DRC 'war zone'

Containing an Ebola outbreak in a "war zone" in the Democratic Republic of Congo is among the most difficult challenges the World Health Organisation has faced, a top official said on Friday.

The outbreak declared in North Kivu province on August 1 poses the same problems as past cases in the DRC, including major logistical hurdles in a volatile country with weak health infrastructure.

But in North Kivu, health workers will have to navigate their response among more than 100 armed groups, 20 of whom are "highly active," WHO's emergency response chief Peter Salama told reporters.

"On the scale of degree of difficulty, trying to extinguish an outbreak of a deadly high-threat pathogen in a war zone reaches the top of any of our scales," he said.

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The outbreak in North Kivu in eastern DRC was declared a week after WHO and the Kinshasa government hailed the end of an Ebola flareup in northwestern Equateur province, which killed 33 people.

Salama underscored that the successful containment of the Equateur outbreak in just 10 weeks required arduous travel around a remote region, tracing and vaccinating people who may have been exposed to the virus.

The same recipe for success is required in North Kivu, but for now health workers do not know what level of access they will have to those affected, given the number of armed groups controlling different areas.

WHO will rely on the UN peacekeeping mission based out of North Kivu's capital Goma and DRC's government to assess how to safely travel, Salama said.

"As the UN, we talk to anyone we need to in order to get access to the civilian population," he said, when asked about outreaches to rebel commanders.

There are 26 suspected cases so far in North Kivu, four of which have been confirmed by laboratory tests as Ebola. Twenty people have died.

"We expect, however, the overall case count will rise in the coming days to weeks," Salama said.

The Ebola strain affecting North Kivu is likely the "Zaire" strain - the same type as hit the northwest.

That means that the new rVSV-ZEBOV vaccine, which gave a significant boost to the response in Equateur, will likely be useful in the new outbreak.

Salama said plans are underway to deploy the 3 000 doses of the vaccine currently in Kinshasa to the east and that vaccination could begin once the presence of the Zaire strain is confirmed.