Cameroon has expelled more than 3,000 Nigerians as part of the fight against Nigeria's Islamic extremists who have launched attacks across borders, officials said.
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.
"We noticed that in the different villages there is a certain population of foreigners and they are hiding behind some Cameroonians and hiding those Boko Haram suspects," Mr Bakary said.
Women, children and men were taken across the border to the Nigerian town of Mubi, he said. A Cameroon government agency has deployed staff to educate people on how to identify extremists.
The UN refugee agency said a camp in Cameroon's Far North Region now hosts about 44,000 people and estimates there are 12,000 unregistered refugees in the region.
In Nigeria, many of those expelled said they were forced out quickly.
"It was a terrible journey. We spent almost six days on the road ...," said Musa Kawuri, a 52-year-old trader. "We initially pleaded with the Cameroonian officials to give us grace of some days," but were put in trucks.
Adamawa State Emergency Management Agency chairman Haruna Hamman Furo said 12,000 Nigerians are expected to arrive from Cameroon.
Everyone expelled would be sent to Yola, Adamawa's state capital, said National Emergency Management Agency camps co-ordinator in Adamawa, Sa'ad Bello.
"Their condition is good," he said. But some refugees said that several people died during their hike to the border.
Boko Haram violence has killed thousands and displaced more than 1.5 million people.