DAKAR (Reuters) – Soldiers in three West African countries unlawfully killed or caused the disappearance of at least 199 people between February and April during stepped-up operations against jihadist insurgents, Amnesty International said on Wednesday.

Security forces in Mali, Burkina Faso and Niger launched fresh offensives this year against militants linked to al Qaeda and Islamic State, who are threatening to overrun vast swathes of the Sahel region south of the Sahara Desert.

Those offensives have led to repeated accusations by human rights groups that security forces have committed atrocities, including executing displaced civilians – charges the authorities have alternately denied or promised to investigate.

Amnesty researcher Ousmane Diallo said it was not clear if the rights abuses, documented in a new report published on Wednesday, were occurring more frequently than in years past but said they took place amid a flurry of activity by national armies after suffering significant losses in militant attacks.

“There is a very large desire to achieve military results,” Diallo said.

In southwestern Niger, 102 people disappeared after being arrested by the army at a market fair and in villages in late March and early April, the report said. Several mass graves were later discovered in the area, it said.

Niger’s Defence Minister Issoufou Katambé said the military and national human rights commission were investigating the events but that the people who had made the accusations “could not produce the proof” when interviewed by investigators.

Government spokespeople in Burkina Faso and Mali did not respond to requests for comment, but Mali’s defence minister issued a statement on Tuesday vowing to investigate repeated allegations against the army, including charges that soldiers killed 43 people during attacks on two villages last week.

Rights groups say investigations promised by governments rarely lead to criminal sanctions.