The United States on Wednesday said it must prevent any cases of Ebola from entering the country from the Democratic Republic of Congo, where an outbreak has already caused a suspected 220 deaths and 900 cases.

The World Health ​Organization has declared the outbreak of the rare Bundibugyo ​strain of ⁠Ebola the third-largest such outbreak on record, and a public health emergency of international concern.

"We cannot and will not allow any cases of Ebola to enter the United States," Secretary of State Marco Rubio said on Wednesday at President Donald Trump's cabinet meeting.

The Trump administration's response, which it says aims to contain Ebola to the outbreak region, is a departure from the 2014 Ebola outbreak when the US treated patients in some of its 13 specialised infectious disease centers.

The US is in talks with Kenya over opening a facility there to quarantine US citizens who are exposed, two US officials told Reuters on ‌Wednesday. Kenya's government has not yet approved the plan.

Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, said patients would be better off in high-containment infectious disease centers in the US or Germany rather than in a newly built location in Kenya.

"I can't imagine that you can build a facility de novo in Kenya to have that same standard that we already have in these NETEC centers," he said.

"They know how to deal with every aspect of it, from taking care of the patients to dealing with the waste, and knowing how to get the technologies there that they might need if someone needs dialysis, for example, or mechanical ventilation."

He also said that such moves would disincentivize doctors from volunteering for the effort.

Last week, a US citizen who was treating patients in the DRC as a medical missionary was confirmed to have contracted Ebola and was moved to Germany for treatment along with five others who were exposed. A seventh person was taken to the Czech Republic.

The Washington Post, citing five people familiar with the US Ebola response, reported last week that the White House ⁠resisted allowing the medical missionary patient to return to the United States, delaying his evacuation and care.

US SAYS IT IS WORKING TO CONTAIN EBOLA

Rubio said the US government has surged assistance to the region. In recent press conferences, officials have said the US government sent a top CDC official to the area and committed millions in funds.

It has also instituted travel bans on people who have travelled into the Democratic Republic of Congo and neighbouring countries, and is screening US citizens at three airports - an effort infectious disease experts say can be ineffective at stopping spread.

The US CDC last week imposed entry restrictions for 30 days on travellers who have been in the DRC, Uganda and South Sudan in the past 21 days, including lawful permanent residents, known as Green Card holders. 

It is also screening Americans travelling from those countries at three US airports. The agency asked staff to volunteer for urgent deployment to support screening at ​the country's entry points.

"What they're doing here is trying to find options that don't require bringing people back to the US if they can, partially because they don't believe they have a lot of bandwidth at facilities in the US," said Chris Meekins, who served as a health official in Trump's first term.

He pointed to people exposed to hantavirus on a cruise who are in quarantine.