The Search for International Terrorist Entities (SITE) Intelligence Group said.
The West African state and its coastal neighbour Togo have suffered a series of attacks in recent years as groups linked to Islamic State and al Qaeda have expanded their presence beyond the Sahel region to the north.
Reuters could not immediately confirm the report independently.
Benin's army Spokesperson Ebenezer Honfoga did not respond to calls and messages.
SITE quoted a statement by JNIM on Thursday saying 70 soldiers were killed in attacks on two military posts in Benin's northeastern Kandi province in the Alibori department, more than 500 km from the capital Cotonou.
United States group SITE tracks online content from militant groups.
The Sahel insurgency took root after a Tuareg rebellion in north Mali in 2012 and spread into neighbouring Burkina Faso and Niger before reaching the north of coastal West African countries such as Benin more recently.
Thousands have been killed and millions displaced by the conflict, which contributed to spurring five military coups in Mali, Burkina Faso and Niger between 2020 and 2023.
Military authorities cut ties with traditional Western allies such as France and the U.S. after the coups and turned to Russia to help in fighting jihadist activity.
--Reuters--