Boko Haram  fighters killed at least two Niger soldiers and wounded four others in an attack on a village near the Nigerian border, army officers said on Friday.

Niger, Cameroon and Chad have all suffered a spillover of violence from Boko Haram’s northern Nigerian strongholds and Niger has arrested at least 1,100 suspected Boko Haram militants this year and has placed its southern region of Diffa under a state of emergency.

But Diffa has suffered at least 57 attacks since February, statistics published by the United Nations on Friday showed.

“We had officers who fell in an ambush set by Boko Haram, who attacked the village of Barwa on Thursday morning. We mourn at least two deaths,” one army officer said.

The militants also looted stores, a second officer said.

At least 150,000 refugees seeking protection from Boko Haram attacks in Nigeria live in Niger’s Diffa region.

A 8,700-strong multinational force with troops from Niger, Nigeria, Benin, Cameroon and Chad, is due to begin operations against the Islamists at end of this month when the rainy season is expected to stop, Chad’s President Idriss Deby said recently.

The force is due to receive U.S. support, including training, worth $45 million.