BUNIA: Ebola deaths in eastern Democratic Republic of Congo have risen to 131 after 26 more suspected fatalities were recorded in 24 hours, authorities said, as the World Health Organization warned over the scale and speed of the outbreak.

Congolese health authorities said the outbreak has now caused 543 suspected cases and 33 confirmed cases in eastern DRC, while neighbouring Uganda has reported two confirmed cases. The outbreak involves the rare Bundibugyo strain of Ebola.

WHO Director-General Tedros Adhanom Ghebreyesus declared the outbreak a public health emergency of international concern on Saturday. He told the World Health Assembly in Geneva that he was deeply concerned about how quickly the disease was spreading.

The outbreak has raised alarm because it spread for weeks without detection in a densely populated region affected by armed violence. Butembo, a major city in eastern Congo, recorded its first two confirmed cases on Monday, according to Jean-Jacques Muyembe, director of Congo’s National Institute for Biomedical Research.

Ugandan authorities have started restricting movement at the Ishasha-Kyeshero border crossing, though officials said the border had not been formally closed. Reuters reporters also said Congolese citizens trying to cross into Rwanda from Goma and Bukavu were being stopped.

The WHO has urged countries not to close borders, warning that such measures could push people toward informal crossings that are harder to monitor.

Ebola spreads through direct contact with bodily fluids from infected people or animals. According to the WHO, the disease has an average fatality rate of around 50 percent.

Unlike the more common Zaire strain, there are currently no approved strain-specific vaccines or treatments for the Bundibugyo strain. WHO-led experts are reviewing possible vaccine options, while the United States has said it is working on a potential monoclonal antibody treatment.

One American has tested positive for Ebola, according to the US Centers for Disease Control and Prevention. The patient and six other exposed Americans are being moved to Germany for care and monitoring.