An upsurge in Boko Haram attacks and returnees from Cameroon are stretching camps for those made homeless by the conflict to breaking point, as the UN warned against forcing people back to northeast Nigeria.

Obinna Orjingene is a doctor for UNICEF in the town of Banki, near the border with Cameroon, where the population has jumped from 32,000 to 45,000 in the last few months alone.

He is part of a small, overworked medical team treating everything from malaria and trauma to malnutrition in the overcrowded camp for the displaced.

"A population of over 40,000 people with just one medical doctor is crazy," he told AFP from Banki by telephone. "It's overwhelming."

But he said the situation is replicated across the remote region.

"I'm quite aware that some camps don't have doctors. There are a lot of challenges."

Rounded up

A total of 889 Nigerian refugees arrived in Banki from the Minawao camp in Cameroon on June 17, prompting the UN high commissioner for refugees to speak out.

Filippo Grandi said he was "extremely worried" by the returns and called them "unsustainable".

The UN refugee agency on Thursday said 887 Nigerians were "rounded up" into six trucks and forcibly returned by Cameroon to camps "dangerously unprepared to receive them".

Like other camps, Banki remains vulnerable to Boko Haram attacks and has been targeted by suicide bombers.

The camp lies inside the old walls of the destroyed city and people, unable to leave because of the militants nearby, depend on handouts for food.

Water and shelter are scarce and children are not in school.

Boko Haram fighters are said to be responsible for the gunfire heard at night.

Forced movement

"In the last month we've had a precipitous return of Nigerian refugees from Cameroon that wasn't necessarily expected," said UNHCR Representative to Nigeria Jose Antonio Canhandula.

"They apparently were informed that the situation was good in Nigeria and they could return.

"We immediately started a campaign to inform them of the real situation. This is not the time to return, because when you return you end up in a camp with much less services."

Cameroon and Nigeria have been battling over refugees for the past year, said Yan St-Pierre, of the Modern Security Consulting Group in Berlin.

In March, the UN said that more than 2,600 Nigerians of an estimated 85,000 who fled into northern Cameroon to escape Boko Haram jihadists had been forced to go home.

In a way, Cameroon is calling Nigeria's bluff, St-Pierre said.

Since December 2015, President Muhammadu Buhari has claimed Boko Haram is "technically defeated" and the government has insisted the group is on the back foot despite attacks.

In the first six months of 2017, Boko Haram has attacked soldiers, staged assaults on military bases, killed scores in suicide bombings and earlier in June launched a major assault on Maiduguri, the capital of northeast Borno state.

"It's a political way of taking them to the word, saying, 'Well, if you've secured the area, then take your population back'," said St-Pierre.

Resurgence in attacks

In March, the UNHCR, Nigeria and Cameroon signed an agreement that outlined a procedure for voluntary returns of refugees.

Yet critics suspect Cameroon is trying to minimise its humanitarian responsibilities to focus on security because of an increase in attacks.

Last week six people were killed in a double suicide attack in Kolofata, a town near the Nigerian border that has been repeatedly targeted.

Cameroon for its part suspects the increase in attacks is down to the infiltration of insurgents among Nigerian refugees and blames Nigeria for not securing the border.

Whatever the reason, for Orjingene, the deteriorating security situation in Cameroon means more people are coming to Banki whether he is ready or not.

"From the look of things, they want all Nigerian refugees back home," he said. "I'm doing my best to save as many lives as I can."