At least 13 Chadian troops and 65 Islamist rebels have been killed in a fierce battle in the remote mountain region of Ifoghas in Northern Mali, Chad's army has said.
Many Islamic insurgents were thought to have sought shelter in the mountains soon after the French-led forces had driven them away from the landlocked West African nation.
The recent death toll is the heaviest for the French and African troops since the launch of the onslaught six weeks ago.
"The provisional toll is ... on the enemy's side, five vehicles destroyed and 65 terrorists killed. We deplore the deaths of 13 of our valiant soldiers," said the military's statement which was read on state radio.
Weeks after the French intervention, African troops have been continually deployed in the country to insulate the regions from the al-Qaida-linked militants.
As part of the operations, Chad has pledged 2,000 troops for the UN-backed African operation. Nearly 1,800 Chadian soldiers have already been deployed to secure the strategic town of Kidal.
The Ifoghas mountains, a desert area in the Kidal region, provide a perfect hideout for the insurgents to launch guerrilla attacks on the Malian and French forces.
Meanwhile, clashes between the Islamists and French-led forces continued in other towns, including Gao.
A deadly car bomb which exploded in the town of Khalil killed five people. The Islamists planted the bomb targeting the secular Tuareg movement's members who have close links with French forces.
"It's simply the continuation of attacks by MUJWA, which will probably want to try more attacks in the coming days. It was sadly predictable and the next attacks will fail just like they did yesterday," French army chief Admiral Edouard Guillard told Reuters, about the Khalil attack.
France dramatically intervened in its former colony in January to stop Islamists from capturing southern parts of the country which include the capital Bamako.
France is expected to withdraw its troops in the coming weeks once the Africans take over.