N'DJAMENA, Chad -- Officials in Chad have arrested 60 people including suspects from Cameroon, Nigeria and Mali in relation to an attack earlier this month in the capital that killed dozens of people and wounded more than 100 others.

Chad prosecutor Alghassim Khamis said Sunday that new details have been uncovered concerning the June 15 attack that saw one suicide bomber blow himself up on foot outside a police station and two others near a police academy. The attack was the first of its kind on N'Djamena, the Chadian capital, and came following threats from the Nigeria-based Islamic extremist group Boko Haram.

"The toll for this double attack is 38 dead today, including the three suicide bombers, and 81 wounded and released and 20 wounded still admitted in the hospital," Khamis said. One person is seriously wounded, he said. The official toll on the day of the attack was 23 dead plus four attackers.

An active terrorist cell has been identified and dismantled, Khamis said, leading to the seizure of "communication materials" and the 60 arrests, which included Chadians in addition to the foreigners.

One of the suicide bombers has been identified, and officials are working on identifying the other two, he said.

Debris recovered from the scene permitted officials to determine that the attackers wore explosive vests made of special black fabric, he said.

"The information received shows that this attack was well planned," he said.

There was no immediate claim of responsibility for the attack but suspicion quickly fell on Boko Haram, the Islamic militant group based in neighbouring Nigeria that had already attacked Chadian villages along the lake dividing the two countries.

Chad has been a major military ally with Nigeria in the fight against the insurgent group, and Boko Haram's leader has publicly threatened the Chadian president with retaliation.

Three days after the attack, Chad said it had launched an aerial assault on Boko Haram positions.