GENEVA (Reuters) - A doctor has become the first probable Ebola case in one of the eastern Democratic Republic of Congo’s most violence-ridden and inaccessible zones, a scenario “we have all been dreading”, the World Health Organization said on Friday.

Since the outbreak erupted on Aug. 1, 103 confirmed and probable cases of Ebola have been identified in North Kivu and Ituri provinces, including 63 deaths, Congo’s health ministry said in an overnight update.

A doctor living in the town of Oicha in North Kivu has been re-hospitalised with Ebola symptoms after his wife was confirmed as having the disease when she traveled to the nearby city of Beni, said Dr. Peter Salama, WHO’s head of emergency operations.

Oicha is almost entirely surrounded by ADF Ugandan Islamist militia, and there are “extremely serious security concerns” following many civilian killings, he said. Aid workers, priests and government officials are held hostage in the area, he added.

More than 100 armed groups operate in all of volatile eastern Congo, including dozens in North Kivu.

The doctor’s initial test for Ebola - which causes vomiting, hemorrhagic fever and diarrhea - had been negative but fresh results are awaited after retesting, Salama told Reuters. The doctor is among 14 confirmed or probable cases among health workers.

So far 97 of the couple’s contacts who may have been exposed to the virus have been identified, and vaccination has begun in Oicha, according to Salama.

“So for the first time really we have a confirmed case and contacts in an area of very high insecurity. It really was the problem we were anticipating and the problem at same time that we were dreading,” he told a news briefing.

WHO and health experts reached Oicha with armed escort by MONUSCO troops this week from Beni along a road classified as a “red zone” in terms of insecurity, Salama said.

“We know from that incident now in Oicha we are going to have to operate in some very complex environments due to security and access concerns.”

Congo has experienced 10 Ebola outbreaks since the virus was discovered on the Ebola River in 1976, altogether killing some 900 people.

In another worrying development, angry youths burned down a health center in the village of Manbangu where vaccinations were underway, after learning of a death from Ebola, Salama said.

Jessica Ilunga, a Congolese health ministry spokeswoman, later said there had been an incident there but denied that the health center had burned. The health minister had held talks with local authorities to help calm the situation, she said.

More than 2,900 people have been vaccinated against Ebola since the outbreak began and another 10,000 doses are currently available, Salama said.

“We are at quite a pivotal moment in this outbreak in terms of the evolution of the outbreak epidemiologically and in terms of the response,” he said.