Boko Haram has stepped up the frequency and intensity of its attacks since the turn of the year, in part to undermine the Nigerian elections.
A devastating attack on the fishing hub of Baga on January 3 has been seen as a turning point in regional cooperation, galvanising neighbouring powers into providing assistance to the Nigerian Army.
Since then, there have been repeated attacks in northern Cameroon, while the Islamists last weekend opened up a new front across the border in Niger, attacking the border region of Diffa.
Niamey on Tuesday evening imposed a 15-day state of emergency in Diffa, where thousands of Nigerians have fled the violence, heaping pressure on food supplies and infrastructure.
A journalist in the area said businesses, government offices and schools were shut as residents sought to flee.
Nigeria maintains the involvement of troops from Chad, Cameroon and now Niger, after the parliament in Niamey approved the deployment of soldiers, is part of an existing agreement.
At the same time, all four countries, whose borders converge on Lake Chad, with Benin, Nigeria's neighbour to the west, agreed to provide 8,700 personnel for an African Union-backed regional force.
Boko Haram leader Abubakar Shekau said in a video published on Monday that the group would defeat the regional forces.
Cameroon's President Paul Biya, however, hit back, saying in a speech broadcast on Tuesday evening that the country would "emerge victorious" from the fight.
"Friendly nations, countries passionate about freedom, the international community, global opinion are with us," he said on state television.
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