Twenty-four Malian soldiers were killed and 29 wounded in an attack on an army patrol in northern Mali on Monday, a spokesman for the army said.
At least 17 terrorists were killed in a counterstrike while hundreds of people were arrested for suspected links to the raid.
Another 29 soldiers were wounded in the raid, which occurred while troops from Mali and Niger were conducting a joint border operation against militants, the Malian Armed Forces (FAMA) said in a statement.
The Malian patrol attacked was in Tabankort, Gao region, while on a joint operation with Niger against militants operating near the border.
No group has claimed responsibility for the attack.
The authorities have not named the assailants or identified which group they belonged to. From strongholds in Mali, groups with al-Qaida and Islamic State links have been able to fan out across the Sahel, destabilizing parts of Niger and Burkina Faso.
The West African country is still reeling from an attack on an army post that killed 54 in early November — one of the deadliest strikes against its military in recent memory, which underscored the increasing reach and sophistication of armed jihadist groups active in the wider region.