Congo's military said an attack late on Tuesday by an Islamic State affiliate — a group known as the Allied Democratic Forces — killed 16 people in the Beni territory in North Kivu province.
The militants struck in response for a joint operation of Congolese and Ugandan armies, which have been battling the group that operates in the border regions of the two countries. Last month, the group attacked Congolese villages near the Ugandan border, killing at least 40 people and burning and looting homes.
The violence has hampered efforts to combat the outbreak of the rare Bundibugyo type of Ebola, which was announced in mid-May in eastern Congo's provinces of Ituri, North Kivu, and South Kivu.
Since then, Congolese authorities have confirmed 60 deaths in the outbreak out of 344 cases.
The number of suspected cases has gone down from 906 to 116. Neighbouring Uganda has 15 confirmed cases, including one death, its health ministry said Tuesday.
The agency's Director-General Tedros Adhanom Ghebreyesus on Wednesday said testing is improving in the struggle against Ebola, with scaled-up laboratory and diagnostic capacity though contact tracing in Congo "is not yet where it needs to be".
"The outbreak had a big head start, and we're still behind," he said.
"But we are catching up."
Tedros spoke a day after returning to Geneva from Congo, where he visited the epicentre of the outbreak.
Experts have said the virus spread for weeks in one of the world's most vulnerable regions before lab testing confirmed it. Resources, including protective gear, have been rushed to the outbreak for a type of Ebola with no approved medicine or vaccine.
At least five people have recovered from the virus, rare signs of hope.
"The true extent of the outbreak remains difficult to assess. Extremely limited testing capacity and difficulties accessing certain areas necessitate interpreting these figures with caution," Doctors Without Borders, said on Monday about the case numbers.
Getting a potential vaccine to the region could take months.
"It's difficult to have an effective vaccine that adheres to the scientific protocol available quickly," Dr. Aruna Abedi, a Congolese epidemiologist who has managed previous outbreaks in the country, told The Associated Press.
While laboratory and diagnostic resources improve for the outbreak, Tedros said the tracing of people who had contact with infected people in Congo is still behind.
"Only about 45 per cent of contacts have been followed up, and to get ahead of the outbreak we need to get that number up to above 90 per cent," he said.
"Insecurity, displacement and mobile populations make contact tracing especially difficult."
