Niger's parliament unanimously authorized sending troops to battle Boko Haram militants as part of a regional force, lawmakers said after a vote late Monday.
Niger, Nigeria, Chad, Cameroon and Benin plan to deploy up to 8,750 soldiers to fight the militants who have killed thousands of people since launching their insurgency in 2009.
Hours before the vote, Boko Haram fighters attacked the southeastern Niger town of Diffa, including carrying out a bombing and raiding a prison.
Boko Haram chief Abubakar Shekau vowed to defeat the regional force in a new video posted to YouTube on Monday. He said a force of that size is small and his fighters can kill them one by one.
He also threatened Chadian President Idriss Deby, whose troops battled Boko Haram fighters last week in Nigeria, Niger and Cameroon.
Nigeria's Independent National Electoral Commission has delayed presidential and parliamentary elections until the end of March, citing the security situation in the country.
The opposition All Progressives Congress protested the decision, and U.S. Secretary of State John Kerry said in a statement that Washington is "deeply disappointed" by the postponement.
President Goodluck Jonathan has come under intense criticism in Nigeria for failing to end the Boko Haram insurgency. Political observers have said he and the ruling PDP party are in danger of losing at the polls.