GOMA, Congo (Reuters) - Mai Mai militiamen attacked an Ebola treatment center at the heart of an outbreak of the disease in eastern Congo on Saturday, killing a policeman and wounding health workers before being repelled by security forces.

The center in Butembo was the same one torched by unknown assailants last week, an attack that prompted medical aid agency Medecins Sans Frontieres to suspend activities in the area.

Aid workers have faced deep mistrust in some areas as they work to contain the outbreak of the deadly hemorrhagic fever, the worst in Democratic Republic of Congo’s history, killing close to 600 people so far.

Efforts to contain the virus have been hampered by a plethora of armed groups operating in Congo’s lawless east.

World Health Organisation (WHO) President Tedros Adhanom Ghebreyesus visited the Butembo center later on Saturday, a statement from the organization said.

“It breaks my heart to think of the health workers injured and the police officer who died in today’s attack, as we continue to mourn those who died in previous attacks, while defending the right to health,” Tedros was quoted as saying.

“But we have no choice except to continue serving the people here, who are among the most vulnerable in the world.”

Butembo major Sylvain Kanyamanda Mbusa said the Mai Mai militants had been successfully beaten back.

“Because of previous attacks, a security system was already in place and attackers were quickly confronted by the police officers guarding the ...center,” he told Reuters.

The facility had resumed operations only a week ago and had been managed by the ministry of health in collaboration with the WHO and United Nations children’s agency.

The Mai Mai take their name from the word for “water” in a local Swahili dialect, because some of their fighters believe magic can turn flying bullets into water.

They comprise several armed bands that originally formed to resist two invasions by Rwandan forces in the late 1990s. They have since morphed into a variety of ethnic-based militia, smuggling networks and protection rackets.

One of the militiamen was wounded in Saturday’s attack and is in custody, Kanyamanda Mbusa said.

On Thursday, MSF accused the Congolese government of failing to contain the epidemic because of an overly militarized response that was alienating patients and their families.