Rwanda closed its border with the Democratic Republic of the Congo, where a deadly Ebola outbreak that began a year ago killed more than 1,803 people.
The closure came after a second death linked to the Ebola virus was confirmed in the densely populated Congolese city of Goma, which is on the porous border with Rwanda.
The World Health Organization, which declared the DRC outbreak of a global health crisis last month, recommended against travel restrictions. It also said the risk of regional spread is "very high."
The DRC presidency office said it regretted what it described as a unilateral decision by the Rwandan authorities to restrict movement at the border, "which is against the advice of the World Health Organization".
Earlier on Thursday, a DRC official said a man who had contact with the second confirmed Ebola case in Goma is in a treatment center after showing signs of the disease.
It was not immediately clear whether the person was a relative of the man who died on Wednesday. He spent several days at home with his family showing symptoms.
If this suspected case is confirmed, it could be Ebola's first delivery of this outbreak in Goma, a city of more than 2 million people.
The growing crisis has resulted in a row in the DRC's ministry of health, which is coordinating national efforts to contain the spread of the virus.
Last week, DRC Health Minister Olly Ilunga resigned in protest of the country's treatment of the Ebola outbreak. Ilunga said international agencies are pushing their government to allow testing of a new vaccine developed by Johnson & Johnson. The row over the vaccine trials began after Ilunga banned clinical trials of the new vaccine in DRC, according to Stat News.
Ebola vaccines are difficult to develop because they need to be tested during outbreaks.
In the previous outbreak in West Africa, one vaccine, produced by Merck, was successfully tested in Guinea. The success of this trial meant preventive vaccines against Merck could be given to citizens in DRC and may contain the outbreak.
But Ilunga argued that trial vaccines in Ebola-affected regions could erode public confidence in the government.
The Merck vaccine requires only one shot, while the new Johnson and Johnson vaccine must be taken in two doses.
Officials and NGOs fear that discrepancies in vaccination schedules – where some people have received one shot, while others have received two – could fuel rumors about vaccines in local communities.
Ilunga also said that delivering two doses would be logically difficult in a region where there is high speed and where people often travel.