US authorities have temporarily banned green-card holders from entering the country if they have traveled to the Democratic Republic of the Congo (DRC), Uganda or South Sudan in the last 21 days.

The order issued on Friday is part of an expanding attempt to prevent Ebola from entering US borders. A previously announced travel restriction blocked only people without US passports who had visited those countries from entering but exempted US citizens and lawful permanent residents.

“HHS [the Department of Health and Human Services] and CDC [the Centers for Disease Control and Prevention] have determined that permitting the director of CDC or other secretarial delegate the discretion to prohibit entry of certain lawful permanent residents is reasonably required in the interest of public health,” the order reads.

The order added that green-card holders may maintain stronger ties to families and communities outside the US than US citizens and nationals, “such that prohibiting their entry is comparatively less burdensome”.

US citizens returning from the DRC, Uganda or South Sudan now have a second point of entry to the US, the CDC said, in addition to Washington’s Dulles airport. The agency said on Saturday it is expanding its enhanced Ebola screening to include the Hartsfield-Jackson Atlanta airport.

It pointed to “resource constraints” for containing a quarantinable disease. Eighteen people are currently in a dedicated quarantine unit at the University of Nebraska after being released from the hantavirus-plagued cruise ship MV Hondius.

“Containing quarantinable communicable diseases on US soil is highly resource-intensive, requiring specialized and isolated facilities with limited capacity,” it added.

In a separate statement, the CDC said that “applying this authority to lawful permanent residents for a limited period of time provides a balance between protecting public health and managing emergency response resources”.

In remarks last week, Marco Rubio, the US secretary of state, said: “Our No 1 objective on Ebola … has to be we can’t have it affect the United States. We can’t have Ebola cases coming here.”

The entry ban on green-card holders coming from the African region is for an initial 30 days.

The World Health Organization raised the risk of the rare Bundibugyo strain of Ebola turning into a national outbreak in the DRC to “very high”. It declared the outbreak in the DRC and Uganda an emergency of international concern.

The WHO says 82 cases have been confirmed so far in the DRC, with seven confirmed deaths, 177 suspected deaths and almost 750 suspected cases linked to the Bundibugyo strain of Ebola.

On Saturday, the Africa Centres for Disease Control and Prevention (Africa CDC) said that 10 African countries are at risk from the Ebola virus.

“We have 10 countries at risk,” said Jean Kaseya, head of the Africa CDC, listing Angola, Burundi, the Central African Republic, the Republic of the Congo, Ethiopia, Kenya, Rwanda, South Sudan, Tanzania and Zambia.

That came as reports emerged that residents of a town at the epicenter of the Ebola outbreak in eastern DRC attacked and burned part of a health center where people were being treated for the virus, and 18 people suspected of infection left the facility.

On Thursday, another treatment center in the town of Rwampara was burned down after family members were prohibited from retrieving the body of a local man.

The bodies of those who died of Ebola can be highly contagious and lead to further spread when people prepare them for burial and gather for funerals. The dangerous work of burying suspected victims is being managed whenever possible by authorities.

Authorities in the north-eastern DRC have banned funeral wakes and gatherings of more than 50 people in an effort to curb the spread of the virus.