A report says half of the militant group's suicide attacks in Cameroon are carried out by children.
The ISIS-affiliated group have launched previously launched attacks in Niger.
Issoufou's opponent, Hama Amadou, has been imprisoned since November 2015 on baby trafficking charges.
Hama Amadou was imprisoned in November for alleged involvement in a baby trafficking ring.
The country is seeking to reduce pressure on its crammed prisons.
The guerrillas arrived in the village of Gogone on foot and opened fire indiscriminately on residents, sources said.
The number of women in Africa who married as children is set to double by 2050.
The Nigerian army have entered Sambisa Forest, thought to be Boko Haram's last stronghold.
Warplanes lead offensive into Sambisa forest, 100 km from village where Boko Haram abducted 200 girls last year.
Chad and Niger military leaders pledge to fight "side by side" with Nigerian army against Boko Haram.
More than 1.2 million people have been displaced within Nigeria and almost 200,000 have fled.
Despite recent defeats, experts have warned that the terror group still pose a significant threat.
South African and former Soviet Union mercenaries training and advising military for pre-election offensive.
Two hundred vehicles transporting troops have entered northeastern Nigeria to take on the Islamist militants.
Jihadists attempt to sneak out of Baga town wearing women's clothes as the military campaign escalates.
Neighboring countries plagued by cross border attacks are weighing in against the insurgent group.
Niger's parliament approves the deployment of more than 3,000 troops to tackle Boko Haram in northern Nigeria.
French reconnaissance flights are beingconducted along Nigerien and Chadian borders as part of wider Sahel strategy.
The death toll from two days of violence in the West African country is now 10.