Niger's President Mamahadou Issoufou on Tuesday told thousands of people protesting at deadly raids by Boko Haram that "Niger will be the tomb" of the Islamists from neighboring Nigeria.

"Nobody attacks Niger without punishment and Boko Haram learned that to its cost last February 6," Issoufou told a crowd after a rally in the capital Niamey. "That day, our defense and security forces crushed Boko Haram."

Cameroon's army says it has killed 86 Boko Haram militants and detained 1,000 people suspected of links to the Islamist group, as central African leaders held talks on how to combat its bloody insurgency.

Five Cameroonian soldiers were also killed during the clashes in the Waza region near the border with Nigeria, defense ministry spokesman Didier Badjeck said Monday.

More than 160 people suspected of having links to Boko Haram have been arrested in Niger's border area with Nigeria which was attacked this month by the Islamist group, police in Niger said Monday.

"We would like to warmly thank the residents of the Diffa region whose assistance has allowed us to arrest more than 160 suspects," national police spokesman Adily Toro said on local television.

Several dozen people suspected of having links to Nigeria's Boko Haram have been arrested in southern Niger since the start of cross-border attacks by the Islamist group a week ago, a local governor said.

"In the region of Zinder, we have a few dozen people whom we arrested for checking. They are suspects," Kalla Moutari told AFP in an interview late Saturday, adding that they were citizens of Niger.

Chad's President Idriss Deby has taken up the fight against Boko Haram at the risk of offending diplomatic sensibilities in Africa, but to the delight of his international allies.

One Western diplomat described Deby, who seized power in 1990, as "first and foremost a fighter," who for years had battled rebels intent on ousting him from power, while at the same time arming those fighting the authorities in neighboring Sudan.

Boko Haram on Wednesday launched a pre-dawn raid in Gamboru, northeastern Nigeria, looking to overwhelm Chadian troops who had pushed them out of the border town.

The military in N'Djamena said the militants were repelled but the counter-attack was an indication of the task facing regional forces aiming to crush the rebellion.

Niger's government on Tuesday declared a state of emergency in the Diffa region along the border with Nigeria, which has been attacked repeatedly by Boko Haram in recent days.

"The state of emergency is proclaimed in the Diffa region for a period of 15 days," a statement read on state radio said. The measure will grant increased powers to security forces, including to carry out searches.

The U.N. food agency on Tuesday voiced concern for the 125,000 Nigerian refugees who have fled to southeast Niger, where Boko Haram militants have launched attacks in recent days.

"The World Food Program is particularly concerned by the attacks in the north of Nigeria which are spreading to Niger, forcing thousands of people to flee," WFP spokeswoman Elisabeth Byrs said.

Niger's parliament voted unanimously on Monday to send troops to Nigeria to join a regional fight against Islamist extremist group Boko Haram, lawmakers said.

"The resolution was passed unanimously. All 102 lawmakers present voted favourably," said lawmaker Mohamed Ben Omar. Another member of parliament said the resolution authorises the country to send some 750 troops to Nigeria.

Nigeria's Boko Haram fighters launched a fresh attack in neighboring Niger on Monday, as parliament in Niamey was set to vote on joining a regional force against the Islamists.

The insurgents raided a prison in the southeastern border town of Diffa, which they first attacked on Friday, but were repelled after a heavy exchange of fire, humanitarian sources said.