An Ebola clinic operated by Doctors Without Borders in war-torn Democratic Republic of Congo came under violent, fiery attack over the weekend—possibly by locals who distrust workers battling the deadly virus, the group said Tuesday.

Congo is in the grip of a stubborn Ebola outbreak that began six months ago and has started to spread beyond the epicenter.

According to the World Health Organization, as of last week, 848 cases had been reported, 79 of them in just the last 21 days. More than 500 people have died of the hemorrhagic fever, which is spread through bodily fluids.

Doctors Without Borders, known as Médecins Sans Frontières, is one of the main medical groups on the ground in Congo, where dozens of rebel groups are fighting for control, putting civilians and medical volunteers in harm’s way.

Late Sunday night, unidentified assailants began throwing stones at a treatment center in Katwa, the nonprofit said.

“They then set parts of the structure on fire, destroying medical wards and equipment. The brother of a patient died while reportedly trying to escape the scene, though the exact circumstances of his death are still unclear,” the organization said in a statement.

The facility was evacuated; four patients with confirmed cases of Ebola and six with suspected cases were transferred to other clinics and all activities have been suspended.

Doctors Without Borders officials said that medical responders have faced mistrust and misconceptions from local residents.

“Although the reasons behind the attack are unclear and such violence is unacceptable, what we know is that the actors of the Ebola response—MSF included—have failed to gain the trust of a significant part of the population,” said Meinie Nicolai, the general director.

“All those involved in this response must change their approach and truly engage with the grievances and fears of the communities.”

The 70-bed facility had assessed and treated more than 600 patients since the outbreak began. “This attack has crippled our ability to respond to what is now the epicenter of the outbreak,” said Emmanuel Massart, the emergency coordinator in Katwa.