Ihsan Ismail has spoken to his family just twice in a month. In the desperate flight from their village outside Mosul they were separated and are now confined to different camps for the displaced.

More than 70,000 people have fled their homes since Iraqi forces launched their offensive on October 17 to retake Mosul, Iraq's second-largest city, from the Islamic State group.

As if living under IS rule for more than two years and being forced from their homes were not enough, now some of the displaced are having to deal with the added burden of being separated from their families.

Security forces say measures are needed to ensure the jihadists do not infiltrate the camps that have sprung up around Mosul to house the displaced. But rights groups are concerned that the restrictions go too far.

Ismail, 18, fled his village of Abu Jarbua east of Mosul shortly after the offensive was launched, and an hour before his parents and little sister Nurhan were able to leave.

Kurdish peshmerga fighters, who are allied with Iraqi federal forces in the Mosul battle, took him to a camp at Khazir but his family was taken to another camp.

He has since only been able to speak to them twice.

"It's been a month like this... I miss them very much," Ismail said. "All I'm asking for is to rejoin them. What's the difference? ... A camp is a camp."

In nearly all of the camps set up to house the displaced, residents are forbidden from leaving and in some cases have had their mobile phones and identity cards confiscated.

"We are at war with terrorists who use all possible means to carry out attacks, and members of Daesh can hide themselves among the displaced and form clandestine cells," Jabar Yaur of the Kurdish interior ministry told AFP, using an Arabic acronym for IS.

- 'De facto detention' -

Human Rights Watch has raised concerns about the restrictions being put on those forced from their homes, known as Internally Displaced Persons, or IDPs.

"In the camps under Iraqi federal control, IDPs have no free movement at all, unless authorities decide to transfer them or send them back home," said Belkis Wille, HRW's senior Iraq researcher.

The situation is almost the same in camps controlled by Kurdish forces, with a few exceptions, like in the Debaga camp south of Mosul where the displaced are allowed to go to the neighbouring village if they leave behind a piece of identification, she said.

"This is a quite disturbing situation, the pattern is very dangerous," Wille said.

"It is de facto detention -- even if it is not detention, in reality it looks like detention."

Ismail is hardly alone -- three of his uncles have also been separated from their families.

Fawaz Khaled, a 42-year-old father of nine, said he and his two brothers also fled Abu Jarbua when Kurdish forces moved in to drive out the jihadists.

After arriving at a peshmerga checkpoint they were taken to Khazir and told their families would join them. They were instead taken to another camp, at Qimawa.

"We are in this situation since October 28 and nobody is listening to us," Khaled said, sipping tea in a tent at Khazir.

Shaima Ismail has not seen her two oldest boys since she also fled Abu Jarbua with her four children.

When they arrived at the peshmerga checkpoint, Mahmud, 16, and three-year-old Amani were allowed to stay with her in Khazir.

But Ahmad, 21, and Mohammed, 20, were taken to the Qimawa camp.

"I have begged them to bring me to my children, or to let them come here, but nobody will give me an answer," she said.

Her boys call just once a week, afraid that camp officials will discover their mobile phone.

"They tell me they are doing OK and then hang up," she said. "The worry is eating away at me."