Chief prosecutor Chaibou Samna told AFP that the trials, on charges of terrorist links, had begun on March 2.
Those facing trial are from several countries including Niger and Mali, Samna said, as well as neighbouring Nigeria where Boko Haram’s deadly insurgency began in 2009 before spreading abroad.
“There have already been convictions and a large number of people freed for lack of evidence,” he added.
“The government has provided the means to transport prosecutors to investigate on the ground” in the Diffa region, close to territory in northeast Nigeria that is the bastion of the armed fundamentalist movement, Samna said.
Boko Haram carried out its first attacks in Niger on February 6, 2015, but has established no base in the mainly Sunni Muslim nation.
The region has also taken in more than 300,000 refugees and displaced people. Thousands of them subsist at the expense of the local population, which is already very poor, and the United Nations has repeatedly asked the international community to step up financial support.