The United States is worried about the outbreak of Ebola in conflict-hit eastern Congo where there are 312 confirmed and probable cases and 191 deaths, a USAID official said on Thursday.

“We are absolutely concerned about the on-going outbreak in the Democratic Republic of Congo,” the senior USAID official,who is working with response teams, told Reuters.

“It is not comparable at this point to the outbreak that occurred in West Africa in 2014,” which spread to nine countries and involved more than 28,000 cases, she says.

But there is worry that the current outbreak was in an active conflict zone in North Kivu, making it hard for health workers to track down and isolate cases, the official say.

“It is occurring in an area of active conflict, so physical insecurity is a persistent challenge and complication to the on-going response efforts,” the official says, speaking on condition of anonymity.

“At this point we are not seeing cases spread across any incredibly large geographic area,” the official says, adding that most cases were in the city of Beni and increasingly in nearby Butembo.

The rate of new cases has accelerated in recent weeks, and neighbouring Uganda has said it will begin to vaccinate some of its health workers against Ebola in case the viral hemorrhagic fever spread from Congo.

The World Health Organization’s committee has said that the outbreak did not yet constitute a public health emergency of international concern.

The USAID official said the United States had deployed over two dozen technical experts to the country to work with Congo’s health ministry since the outbreak was first reported in August.

Since then, the United States had also deployed disaster and health experts from USAID and the U.S. Centers for Disease Control and Prevention.

The official declined to give specifics about responses and funding because of the security threat from armed groups.

Congo has suffered 10 Ebola outbreaks since the virus was discovered near its eponymous Ebola River in 1976. The official said lessons learned from the West Africa Ebola crisis were currently being applied in Congo, including improved approaches to treatment and isolation that allow for better patient care.