The UN's refugee agency on Tuesday urged Cameroon and other nations not to expel Nigerians who have fled their homes amid fighting between Boko Haram Islamist rebels and government troops.
"With the recent escalation of violence in northeast Nigeria, UNHCR is today advising all states against forced returns of people to the region," spokesman Dan McNorton told reporters.
"We are also urging that borders be kept open for Nigerians fleeing the country and who may be in need of international protection," he added.
UNHCR's concerns focus on Cameroon, the choice of refuge for most of the 10,000 Nigerians who have fled during a sweeping government offensive against the rebels that started in May.
McNorton said UNHCR was alarmed by reports earlier this month that 111 people had been forced by Cameroon's security forces to return to Nigeria from a border village in Cameroon.
Fifteen people were killed in the border zone during the incident, although it was not clear who was responsible, he said.
The remaining individuals fled back to Cameroon and were detained, and UNHCR was working with officials there to assess whether they were refugees.
"In light of the security situation in northeastern Nigeria, people fleeing are likely to meet the criteria for refugee status," said McNorton.
Chad and Niger have also taken in Nigerians escaping the fighting, but there have been no reports of forced returns from those countries, he said.
Inside Nigeria, meanwhile, an estimated 5,000 people have fled their homes.
"But as humanitarian access has been hampered by the attacks, UNHCR believes the actual number of people affected could be significantly higher," underlined McNorton.
Boko Haram, thought to be a fragmented group with a murky leadership structure, rose up against the government four years ago.
Its fighters have attacked churches, mosques, the security forces and schools across northern and central Nigeria, Africa's most populous country and top oil producer.
Besides condemning the Islamists' bloody campaign, human rights groups have also slammed government troops for killing civilians and for other violations in the conflict zone.
The conflict has claimed thousands of lives since 2009.