PARIS (AP) — French President Emmanuel Macron has vowed to combat illegal immigration on the French island of Mayotte in the Indian Ocean.

Macron has started a four-day visit to French overseas territories on Tuesday. On Mayotte, he met with police and military units in charge of an operation that aims to send 25,000 migrants back to their countries this year.

Mayotte is the only part of the Comoros archipelago that voted to remain part of France in a 1974 referendum. It sees migrants arrive from neighboring islands.

Macron will also address economic development issues on the poverty-stricken island.

The French government announced an emergency plan last year following weeks of street protests against increasing violence, illegal immigration, high unemployment and an economic crisis.

Macron will next visit Reunion island.