Cameroon authorities forced nearly 900 refugees back to northern Nigeria against their will this week, violating an agreement between the two countries to shield thousands from Boko Haram violence, the United Nations said on Thursday.
The Cameroonian government denied force had been used to send refugees home and said repatriation had taken place with the refugees' consent.
About 887 Nigerians, most of them children, were ferried across the border on Tuesday night in trucks provided by the Nigerian military and Cameroonian police, the U.N. refugee agency (UNHCR) said.
"The involuntary return of refugees must be avoided under any circumstances," U.N. High Commissioner for Refugees Filippo Grandi said in a statement. "Returns to Nigeria put a strain on the few existing services and are not sustainable at this time."
If done forcibly, the move counters an agreement signed by Nigeria, Cameroon and the UNHCR in March stating that Nigerian refugees in Cameroon will not be forced back to a remote region ripped apart by violence and where humanitarian efforts are severely stretched.
"There was no forced repatriation of 887 Nigerian refugees from Banki to Borno State in Nigeria. It happened with their consent," said Cameroon's government spokesman Issa Tchiroma Bakary. "Cameroon respects the law and its international commitments."
The Nigerian official responsible for humanitarian activities in the Boko Haram-affected northeast was not immediately available for comment.
Boko Haram has forced more than two million people to flee during its seven-year campaign to create an Islamic state in northeast Nigeria. More than 85,000 Nigerian refugees reside in Cameroon's Far North region.
Over 11,000 have returned to Nigeria this year as camps in Cameroon struggle to accommodate them. It is unclear how many of these have been forced to leave, but the U.N. has warned against repeated attempts to send refugees home against their will.