A group of 11 army officers, led by Baradine Berdei Targuio, president of the Chadian Organisation of Human Rights, were behind the attempt, said a government statement.

The security services arrested those responsible some time from December 8, 2022, the statement added.

Outlawed demonstrations were held on October 20 to mark the date when the military junta had initially promised to cede power -- a timeline that has now been extended by two years.

Around 50 people died, including 10 members of the security forces, according to an official toll.

But opposition groups say the real count was much higher, and allege unarmed civilians were massacred.

Strongman General Mahamat Idriss Deby Itno accused the demonstrators of "insurrection" and attempting to stage a coup.

The authorities have said 601 people, including 83 minors, were arrested in the N'Djamena area alone and taken to Koro Toro, a high-security jail located in the desert 600 kilometres (375 miles) from the capital.

A total of 401 people were put on trial in a court in the jail, in proceedings that lawyers boycotted in protest.

After a four-day trial, 262 were jailed for between two and three years, 80 were given suspended terms and 59 were acquitted, the prosecutor said.

Deby, 38, took power when his father, Idriss Deby Itno, who had ruled the arid Sahel state for 30 years, died during an operation against rebels in April 2021.