The WHO said at least one person has died after contracting Ebola in Congo's northeast.
The DRC previously faced an outbreak of the virus in 2014 which left over 40 people dead.
An Ebola outbreak in West Africa in 2014-15 killed over 11,000 people.
Ebola outbreak declared in DR Congo by WHO
What is Ebola virus disease?
Ebola is a kind of hemorrhagic fever caused by the Ebola virus. It starts with mild symptoms like fever, sore throat, headache and goes on to internal and external bleeding.
Patients in serious cases, generally die within 6-16 days after symptoms appear, making it a high death risk disease killing between 25 and 90 percent of those infected.
The virus spreads through body fluids.
9 people suspected of being infected with Ebola
Overall, nine people are suspected contracting Ebola in the DRC.
Of these, three people have died, of whom one case of Ebola was confirmed through laboratory tests.
The WHO said people started falling ill after April 22 in the DRC's far north Bas-Uele province, a remote and thickly forested region some 1,300km from the capital Kinhasa.
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WHO: DRC is facing "public health crisis"
The WHO said the Ebola outbreak in the DRC is "a public health crisis of international importance."
It has dispatched a team of experts, which includes epidemiologists, biologists and hygiene specialists, to the affected region.
There is no specific treatment for the virus.
The Ebola virus can spread quickly between people unless preventive measures are taken. It's fatal in nearly 90% of cases.
Crucial to find who the suspected patients had contact with
"It's very important to find all the possible contacts of people who have been infected, who has been in contact, and see whether there is a possible continuation of infection and limit it as much as possible," the WHO said.
No need for panic, DRC has experience in tackling Ebola
The outbreak is a worrying development.
However, as the BBC's Tulip Mazumdar notes, the DRC "has stamped out more Ebola outbreaks than any other place on earth. It is well practiced in fighting the deadly virus."
The DRC has experienced nine outbreaks since 1976.
It took West Africa two years to deal with the 2014 Ebola outbreak. The DRC took four months.
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