ABUJA (Reuters) – The United Nations refugee agency (UNHCR) said on Tuesday it is concerned about Cameroon forcing thousands of refugees to return to northeast Nigeria, an area struggling with insurgency and facing a potential famine.

UNHCR teams in Nigeria have heard and documented accounts of Cameroonian troops returning refugees against their will, despite an agreement between the two countries that any such returns should be voluntary.

Babar Baloch, UNHCR spokesman, told a press briefing the agency was “particularly concerned” that more than 2,600 refugees, many of whom had fled militant group Boko Haram, had been sent back to Nigerian border villages since the start of the year.

“UNHCR calls on the government of Cameroon to honor its obligations under international and regional refugee protection instruments, as well as Cameroonian law,” he said.

Issa Tchiroma Bakary, Cameroon government spokesman, told Reuters the allegations were not true. “I formally deny this rumor that Cameroon forced Nigerian refugees to return to Nigeria,” he said.

Jihadist group Boko Haram has displaced over 2 million people in Nigeria since 2009, conducting an insurgency aimed at creating an Islamic caliphate in the northeast of Africa’s most populous nation.

Partly due to the conflict, the U.N. warned last month that aid agencies must get food to nearly 3 million people by July to avert a famine in the Lake Chad region – shared between Cameroon, Niger, Nigeria and Chad – caused by drought, chronic poverty and Boko Haram.

Cameroon says it has stuck to the terms of an agreement signed on March 2 with Nigeria and the UNHCR for “the voluntary return of Nigerian refugees when conditions were conducive”.

“Cameroon is respecting its engagements,” Bakary said.

(Reporting by Alexis Akwagyiram in Abuja and Sylvain Andzongo in Yaounde; Edited by Vin Shahrestani)