As Chad grapples to secure islands on Lake Chad used by Nigeria’s rebel group Boko Haram as hideouts and bases to launch attacks, Chadian forces have reportedly killed seven of the rebels in a clash on Wednesday, a security source said.

Last week Chad said it killed 117 Boko Haram fighters as part of a two-week offensive on the lake that borders Nigeria, Niger and Cameroon, according to Reuters.

"Boko Haram fighters in boats opened fire on our forces on the island of Tchoukou Dallah. Seven of their fighters were killed and there were others wounded," said a security source who declined to be named. There was no independent confirmation.

Meanwhile, thousands of soldiers have reportedly been deployed to tackle the militants whose six-year-old insurgency has killed hundreds in recent months.

Reuters says Boko Haram militants have stepped up attacks in countries around the lake in recent months in response to a regional offensive. It has also adopted the name Islamic State's West Africa Province (ISWAP) after pledging allegiance to the militant group that controls parts of Syria and Iraq.