Chadian lawmakers voted on Wednesday to indefinitely extend the mandate of troops participating in a regional effort to combat Nigeria’s Boko Haram Islamist militants until the joint mission was completed.

Chad has deployed some 2,500 troops to Nigeria, Cameroon and Niger in a joint operation aimed at tackling the Islamist group whose six-year insurgency in northern Nigeria, had threatened the stability of countries in the Lake Chad region.

Boko Haram fighters, who had seized large swathes of northern Nigeria and carried attacks in neighbouring countries including raids and kidnappings, have been beaten back by the joint military campaign.

“The national assembly authorises the prolongation of Chad’s military engagement in Nigeria and Cameroon,” the resolution voted in parliament said. The national assembly had voted on January 17 to deploy the troops for a four months period.

Chadian opposition parties had unsuccessfully voted against the bill demanding more explanations from the government on the financial and human cost of the deployment