“Three suicide bombers blew themselves up in three different places at the weekly market on Loulou Fou, an island in Lake Chad,” the source told AFP, speaking on condition of anonymity.
He said the explosions had “killed 30 people”, including the attackers, and wounded more than 80.
N’Djamena on November 9 declared a state of emergency in the flashpoint Lake Chad region, which also straddles Nigeria, Cameroon and Niger and is frequently targeted by Boko Haram Islamists who this year declared allegiance to the Islamic State.
The decree granted the governor of the remote region the authority to ban the circulation of people and vehicles, to search homes and to seize arms.
In recent months, Boko Haram Islamists have stepped up attacks and suicide bombings on Chadian villages in the lake that lie close to the frontier with Nigeria.
The deadliest attack on Chad’s side of the lake took place on October 10, another triple suicide, which killed 41 people at Baga Sola, according to N’Djamena.
Since the start of the year, the Chadian army has been on the front line of a regional military operation against Boko Haram, whose attacks have spread from northeast Nigeria, its traditional stronghold, to the country’s three Lake Chad neighbours.
Boko Haram has been hit hard by the offensive, losing territory, but has launched a wave of attacks and bombings in response.
The jihadists, believed to be hiding out in Nigeria’s Sambisa forest and the lake’s many islands, are held responsible for 17,000 deaths and for making 2.5 million people homeless in their six-year campaign of violence.