Nigerien and allied forces from neighbouring states killed 75 Boko Haram insurgents in security operations earlier this week in the region where the borders of Niger, Nigeria and Chad converge, Niger’s defence ministry said.

The Islamist Boko Haram insurgency erupted in northeastern Nigeria in 2009 and continues to grind on, with attacks frequently spilling over into Chad, Niger and Cameroon a little further to the south.

The operations on Monday followed a series of Boko Haram attacks on military positions near the southeastern Nigerien border town of Diffa, the ministry said in a statement late on Tuesday.

It said 25 insurgents were killed in fighting around 75 km (46.6 miles) south of Diffa and a further 50 in air and artillery strikes by joint Nigerien, Nigerian and Chadian forces in the Lake Chad area.

It added that weapons were seized and a logistics base used by the insurgents destroyed.

The U.N. refugee agency said on Tuesday violence in northwestern Nigeria had forced about 23,000 people to flee into Niger since April and raised concerns about the deteriorating security situation in that region.