"Iraqi security officers are routinely denying relatives of suspected Islamic State (IS) members the security clearance needed to obtain identity cards and other documents, " HRW said.

"Denying government benefits because of perceived family relationships instead of individual security determinations is a form of collective punishment prohibited under international human rights law."

The New York-based rights watchdog said in a statement that without proper documentation these individuals cannot move freely in fear of arrest, nor can they apply for jobs or welfare benefits.

Children denied birth certificates "may be considered stateless and may not be allowed to enrol in school", while widows who fail to get death certificates for their husbands cannot inherit or remarry, it said.

"Iraq's security forces are marginalising thousands of families of (IS) suspects by depriving them of the basic documents they need to rebuild their lives," said HRW's deputy Middle East director Lama Fakih.

"Unless this collective punishment stops, the authorities will be further destabilising the situation in Mosul and other former ISIS-held cities," she said using another acronym for IS.

HRW said it had interviewed 18 people in Mosul, including lawyers, aid workers and security officials, for its report since late January.

"The Iraqi government has valid security concerns that ISIS members sought for serious crimes should not be able to get fake identity documents," Fakih said.

"But keeping women and children who did nothing wrong beyond having a relative join ISIS out of work, out of school, and in fear of arrest every day will do nothing to foster reconciliation in Iraq.".

Iraqi forces announced the total defeat of IS in the country in December after a punishing campaign to oust the group from territory it seized in 2014, including Iraq's second city Mosul.