Boko Haram militants have kidnapped 21 civilians in the north of Cameroon near the Nigerian frontier, police and local officials said on Thursday.

Since it began a decade ago, Nigeria’s Boko Haram insurgency has killed more than 27,000 people, displaced some two million, and spilled over into neighbouring Cameroon, Chad and Niger.

“Boko Haram attacked around 2300 (22:00 GMT) in Mbreche district, about 30 kilometres (20 miles) from the Nigeria border. They kidnapped 21 people, but four managed to escape,” a local official said.

A police official confirmed the number of kidnapped people. Security forces were hunting for the 17 captives, the official said.

Since 2014, Cameroon says attacks on its territory have caused “several thousand” deaths. The insurgency has forced more than 250,000 people to flee their homes as well as trigger an influx of 60,000 Nigerian refugees.