BUTEMBO, Congo (AP) — Militia members attacked an Ebola treatment center hours after another attack killed a staffer with the World Health Organization, a Congolese official said Saturday.

Butembo city’s deputy mayor, Patrick Kambale Tsiko, told The Associated Press that the attackers armed with machetes tried to burn down the center in Katwa district overnight. Military and police guarding the center killed one militia member and detained five others, he said.

Such violence has deeply complicated efforts to contain what has become the second-deadliest Ebola virus outbreak in history, with the number of new cases jumping each time treatment and prevention work is disrupted.

An attack on Friday on a hospital in Butembo killed an epidemiologist from Cameroon who had been deployed to the outbreak in eastern Congo.

Tsiko cited witnesses as saying the attackers wrongly blamed foreigners for bringing the deadly virus to the region.

This outbreak now has more than 1,300 confirmed and probable cases, including 855 deaths, since being declared last August.

The number of new cases has risen alarmingly in recent weeks after other attacks, leading the WHO to convene an expert committee that decided the outbreak, while of “deep concern,” is not yet a global health emergency .

Attacks by rebel groups and community resistance have posed serious challenges to containing Ebola.