Cameroon has expelled more than 3,000 Nigerians as part of the fight against the extremist group Boko Haram, which is based in Nigeria and has carried out attacks across borders, officials said Tuesday. People suspected of being Boko Haram fighters disguised as refugees with explosives hidden in their luggage were arrested at a camp in northern Cameroon on Monday, a government spokesman said Tuesday. The authorities also arrested hundreds of Cameroonians and Nigerians accused of collaborating with Boko Haram, said Midjiyawa Bakary, governor of Cameroon’s Far North region. They deported Nigerians who said they were refugees but were not staying at refugee camps and lacked identification papers. The United Nations refugee agency says a camp in the Far North region now hosts about 44,000 people and estimates that there are 12,000 unregistered refugees in the area.