Burundi launched a drive Tuesday to register all foreigners, sparking fears among overseas nationals that the scheme could be a pretext for government surveillance.
All non-Burundians in the crisis-hit country will be required to report to border police offices in the coming two months, according to a public security ministry spokesman.
Several foreigners told AFP they feared it was a pretext to track them, and Rwandans said the process could lead to their community being victimised.
But Public Security Minister Alain-Guillaume Bunyoni insisted last month that the move was aimed at granting foreigners a biometric ID card.
Foreign nationals — who also include people from West Africa including Congolese, as well as Indians — will be required to attend police stations in person and carry their travel documents.
Thousands of Rwandans who lived in Burundi have fled the country since the start of the crisis after several arrests within their community.
Relations between Burundi and Rwanda are at a low ebb, with Bujumbura and the United Nations accusing Kigali of supporting Burundian rebels.
Officials in the Burundian Capital, Bujumbura, on Monday showed a mass grave to the public for the first time, confirming reports that dozens of people had been buried in such graves since political violence erupted last year.
The remains of three people were dug up from the grave in Mutakura neighbourhood, an opposition stronghold in the presence of the media.
About 30 people are believed to have been buried there, Bujumbura Mayor, Freddy Mbonimpa, said.
The grave was believed to date from April or May of 2015, when protests erupted against the announcement by President Pierre Nkurunziza that he would seek a third term in office.
Defying the constitutional two-term limit, Nkurunziza won an election boycotted by the opposition in July.
More than 400 people have been reported killed in protests, attacks by police and the armed opposition, according to the UN.
The previous death tolls however do not include whatever people may be found in mass graves.