DAKAR, Senegal — Cameroon’s military has forcibly deported at least 100,000 Nigerian asylum-seekers in the past two years in an effort to slow the spread of Islamic extremism, Human Rights Watch said Wednesday.

The deportations defy a request by the UN Refugee Agency to protect refugees and not force any returns to Nigeria, the rights group said. Nigerians being sent back are facing more violence, destitution, and further displacement, it said.

‘‘Since early 2015, Cameroonian soldiers have tortured, assaulted, and sexually exploited Nigerian asylum seekers in remote border areas, denied them access to the UN refugee agency, and summarily deported, often violently, tens of thousands to Nigeria,’’ Human Rights Watch said.

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