By Madjiasra Nako and Joe Penney
N'DJAMENA/GAO (Reuters) - Ten Chadian soldiers were killed in combat in northern Mali's mountainous border with Algeria where Islamist rebels regrouped after losing urban areas to a French-led offensive, Chad's army said on Sunday.
The latest Chadian fatalities came in an area of the Adrar des Ifoghas mountains where 13 Chadian soldiers were killed in clashes on Friday that centered around what one senior commander said was a rebel base of "significant importance". At least 93 rebels have been killed in fighting in the area so far, Chad's army said.
The casualties, the heaviest by African troops since a campaign against al Qaeda-linked Islamist rebels began six weeks ago, highlight risks that the French-led coalition becomes entangled by guerrilla war as it helps Mali's weak army.
"In the course of the clean-up operations, the bodies of 28 other terrorists were found in the combat zone ... Ten more of our soldiers fell," said a statement from the army general staff read on state radio.
"The final toll from the clashes ... and clean-up that followed is as follows: 93 terrorists ... on the side of the enemy. We deplore the deaths of 23 soldiers and 30 wounded," the statement said.
France intervened in its former West African colony last month to stop a southward offensive by Islamist fighters who seized control of the north last April.
After quickly driving the rebels out of major urban areas, France and its African allies have focused on the remote northeast mountains and desert - an area the size of France - that includes networks of caves, passes and porous borders.
They believe some of eight French hostages held by al Qaeda-linked groups are being kept in the area.
Rebels have continued to stage bombings and raids mainly targeting Mali's poorly trained and equipped army in northern cities - including their former strongholds of Gao and Kidal.
In Gao, which has seen a series of attacks over two weeks, French and Malian forces showed journalists arms and ammunition seized since the start of operations to retake the north.
Laid in blazing sun at Gao's airport, now a base for the French, were hundreds of weapons and thousands of rounds of ammunition, from old Russian rockets to shiny Chinese bullets.
"This is a campaign to finish off the jihadists once and for all"," the head of Malian forces Colonel Didier Dacko said. "It's when the shooting ends, when the population is no longer reporting movements by the jihadists, those will be the signs that the situation has improved"
Troops from neighboring African nations, including 2,000 Chadians, have deployed to Mali and are meant to take over leadership of the operation when France begins to withdraw forces next month.
(Additional reporting by Emmanuel Braun in Gao; Writing by Joe Bavier; Editing by Jason Webb)