(NEW YORK) -- The Department of Homeland Security on Wednesday announced new arrival restrictions for flights carrying people who were recently in Democratic Republic of Congo, Uganda or South Sudan amid the Ebola outbreak in the region.
All flights -- excluding those operated by the Pentagon -- departing after 11:59 p.m. ET on Wednesday carrying passengers that were in the named nations within 21 days of attempted entry into the U.S. will be ordered to land at Washington-Dulles Airport in Virginia, the notice said, where "enhanced public health measures are being implemented."
The Ebola outbreak in the eastern DRC had caused 139 suspected deaths with nearly 600 suspected cases as of Wednesday, according to an update from World Health Organization Director-General Dr. Tedros Adhanom Ghebreyesus.
Tedros said cases of Ebola have been reported in several urban areas of the eastern DRC amid the ongoing outbreak, including the major cities of Goma and Bunia, and that at least two cases and one death have been recorded in neighboring Uganda's capital, Kampala. Cases have also been reported among health workers, according to Ghebreyesus.
At least 51 cases have so far been confirmed in the ongoing outbreak.
The DHS flight restriction notice said that while South Sudan has not reported any confirmed cases in the current outbreak, "It is considered at high risk because of its close border with affected areas in eastern DRC and Uganda, limited healthcare infrastructure and cross-border population movement."
The outbreak was first detected in the DRC's northeastern province of Ituri, with cases officially confirmed by the health ministry on May 15. It marked the 17th outbreak of Ebola virus disease in the DRC, which is Africa's second-largest country and its fourth-most populous nation.
The WHO convened an emergency committee on Tuesday night, following Tedros' declaration of a public health emergency of international concern on Sunday -- one level below a pandemic in the United Nations agency's alert system.
It was the first time a WHO chief had declared such an emergency before convening the emergency committee. After the meeting, the committee agreed that the outbreak did not meet the criteria of a pandemic emergency, which was applied to the global COVID-19 outbreak.
Anais Legand, the WHO's technical officer for viral hemorrhagic fevers, said on Wednesday that the Ebola outbreak may have started a couple of months ago and that investigations are ongoing.
"Our priority is really to cut the transmission chain by implementing contact tracing, isolating and caring for all suspects and confirmed cases," she said.
The current outbreak is caused by the Bundibugyo virus, a rare variant of Ebola for which there are no approved vaccines or therapeutics and which requires different diagnostics than other variants. Case fatality rates for previous Bundibugyo outbreaks have ranged from 30% to 50%, according to the WHO.
Among the confirmed cases is an American, Dr. Peter Stafford, who contracted the disease while working in the DRC. Stafford was flown out of the DRC and is now hospitalized in Berlin's Charité University Hospital.
Matt Allison -- the executive director of Serge, the Christian missionary group Stafford works for -- told ABC News on Wednesday that the doctor has been receiving monoclonal antibodies during his hospitalization and is "responding quickly."
Dr. Satish K. Pillai, incident manager for the Centers for Disease Control and Prevention's Ebola response, confirmed at a CDC press conference on Tuesday that genetic testing from this outbreak shows it is similar to the "genetic fingerprints" from outbreaks in 2007 and 2012, meaning there are diagnostic tools available that can detect this strain of Ebola.
Pillai said on Monday that the agency had activated its Emergency Operations Center through its country offices in the DRC and in Uganda, and is deploying technical experts that have been requested from Atlanta headquarters.
The risk to the U.S. general public remains low, Pillai said.
Also on Monday, the CDC introduced entry restrictions on non-U.S. passport holders that had been in Uganda, the DRC or South Sudan in the previous 21 days before attempted entry into the U.S.
ABC News' Eric M. Strauss, Mary Kekatos and Morgan Winsor contributed to this report.