Out of "267 people who were arrested, 12 were sentenced on Monday to 20 years in prison and 231 others to terms ranging from 10 to 15 years," Justice Minister Djimet Arabi told AFP.

Twenty-four minors who had been detained were released, Arabi said.

The sentences were pronounced by a "special criminal court," which also handed down life sentences in absentia against nearly a dozen rebel leaders living outside Chad, including their chief Timan Erdimi, he said.

An armed group opposed to Chadian President Idriss Deby Itno, the Union of Resistance Forces (UFR), is based in the desert of southern Libya.

In February, UFR fighters crossed into northeastern Chad in a column of 40 pickups before they were halted by several strikes from French warplanes based near the Chadian capital N'Djamena.

France is the former colonial power in Chad and an ally of Deby, who seized power in 1990 with French help.

French forces are stationed in Chad as part of a strategy to fight jihadism in the Sahel.

The French military said at the time of February's incident that the Chadian air force had carried out strikes to try to repel the rebels before asking the French to intervene.

The insurgents had crossed 400 kilometres (250 miles) of Chadian territory before being halted, France said.

The Chadian army moved in after the strikes, later announcing that it had captured more than 250 people.

Arabi said the special court had convened in Koro Toro, a prison located in the desert in the north of the country.

Proceedings began on August 20, the minister said.

"The rebels were sentenced yesterday after a fair trial," he said.