A new report has revealed that there is ample evidence that jihadi fighters from the Sahel region have crossed into Nigeria through the Benin Republic border.

The report was released on Wednesday by the Clingendael Institute, a Dutch think-tank, which has done extensive research in the Sahel.

The Sahel region has seen a surge in terrorist attacks and extremism, particularly in countries such as Mali, Burkina Faso, and Niger Republic.

The tri-border region in these countries has been particularly affected, with terrorist groups like Al Qaeda and the Islamic State expanding their influence and carrying out attacks on government forces and civilians.

Increasing military coups in recent times have also worsened insecurity, with the West African nations severing ties with the US and France, and turning to Russia for help.

Benin, which shares borders with Nigeria, Niger Republic, and Burkina Faso, has also seen an uptick in violent extremism in its northern region.

"That violence has now seeped into Nigeria," the Clingendael Institute said.

According to the report, banditry is re-emerging in zones controlled by the Jama'a Nusrat ul-Islam wa al-Muslimin, JNIM, a militant jihadist organisation, in Beninn and that the bandits seem to have Nigerian connections.

The report said the extremists have settled in Kainji Lake National Park in Niger and Kebbi states.

"Evidence suggests this involves Sahelian extremists (likely JNIM). Another group would be Darul Salam - a group linked to Boko Haram, if not fully affiliated -- with an open attitude towards bandits," the report said.

"Bandits and unidentified armed groups are known to move towards Kebbi State from Sokoto. It is alleged that these include various Darul Salam fighters with links to the Sahel."

The Clingendael report said it is unclear what the motive of the Sahel extremists in the park is and what their relationship with other armed groups there will be.