Witnesses say an explosion has occurred at the central market in Chad's capital.

The blast Saturday morning came less than a month after suicide bombers on motorcycles attacked two buildings in N'Djamena, killing nearly 40 people in the first assault of its kind since Islamic militants threatened the country earlier this year.

In late June, two more suicide bombings in N'Djamena killed 11 people including five police officers.

Details and casualty information for Saturday's attack was not immediately available.

Suspicion for the earlier attacks fell on Boko Haram, the Islamic militant group based in neighboring Nigeria that has also attacked Chadian villages along the lake dividing the two countries.

Chad has been a major participant in the fight against Boko Haram, which has publicly threatened Chad's president with retaliation.