The new deaths bring to 131 the fatalities associated with the outbreak in eastern DRC.
There have been 516 suspected cases and 33 confirmed cases in DRC, according to a daily bulletin published by health authorities, and two confirmed cases in neighbouring Uganda.
WHO Director-General Tedros Adhanom Ghebreyesus declared the outbreak of the rare Bundibugyo strain of the virus a public health emergency of international concern on Saturday, the first time a WHO chief has done so before convening an emergency committee.
The outbreak has alarmed experts because it was able to spread for weeks undetected across a densely populated area ravaged by widespread armed violence.
A 2018-20 outbreak in eastern DRC was the second deadliest on record, killing nearly 2300 people.
Butembo, a city of hundreds of thousands of people in North Kivu province, recorded its first two confirmed cases on Monday, Jean-Jacques Muyembe, director of Congo's National Institute for Biomedical Research (INRB), told Reuters.
Ugandan authorities have started restricting movement across the Ishasha-Kyeshero border crossing to limit further spillover of the virus, Ambrose Amanyire Mwesigye, a local government official, told Reuters.
He said the border was not closed but did not explain who might be allowed to cross.
Further south, Congolese people trying to cross into Rwanda from the cities of Goma and Bukavu were being stopped at the border, Reuters reporters said.
Rwandan officials could not immediately be reached for comment.
The WHO had on Saturday urged countries not to close their borders, saying this could lead to informal border crossings that are not monitored.
Ebola, which spreads through direct contact with bodily fluids from infected people or animals, has an average fatality rate of about 50 per cent, according to the WHO.
"I'm deeply concerned about the scale and speed of the epidemic," Tedros told members of the World Health Assembly in Geneva on Tuesday, citing the number of cases being reported in urban areas and among healthcare workers.
Six tonnes of supplies, including personal protective equipment, were set to arrive in DRC on Tuesday, as well as the 12 tonnes that had already been delivered, said Anne Ancia, the WHO's representative in DRC.
Unlike with the more common Zaire strain of Ebola, there is no approved virus-specific therapeutics or vaccine for the Bundibugyo strain.
The US, which said it had mobilised an initial $US13 million ($A18 million) to respond to the outbreak, is working to develop a monoclonal antibody therapy as a potential treatment, the CDC said on Monday.
A panel of experts led by the WHO will also meet on Tuesday to discuss if there are any vaccine options to help tackle the outbreak.
The WHO's Ancia said Merck & Co's Ervebo was one candidate but that it would take two months to be available.
The US officially left the WHO in January in a move President Donald Trump said was motivated by the organisation's poor management of the COVID-19 pandemic.
Ancia said the WHO had been working "very well" with the US government on the Ebola outbreak but reductions in health funding had had a "tremendous impact" on the organisation's ability to counter the disease.
Under Trump the US has slashed global health funding, and other major donors have also made cuts.
