Kuwaiti police torture and sexually abuse transgender women - individuals born male but who identify as female - a Human Rights Watch (HRW) said on Sunday, urging the Gulf state to protect them from violence and investigate claims of brutality.

A Kuwaiti Interior Ministry spokesman declined to make an immediate comment on the report, saying he might give a reaction after the report was released.

The HRW report, titled “'They Hunt us Down for Fun': Discrimination and Police Violence against Transgender Women in Kuwait," documents physical, sexual and emotional abuse and persecution of transgender women by police.

It said the government should repeal a 2007 law which criminalises "imitating the opposite sex," and hold police officers accountable for misconduct.

The report - based on interviews with 40 transgender women, and ministry of interior officials, lawyers, doctors and civil society figures - said police have a free rein to determine whether a person's appearance amounts to "imitating the opposite sex" since no there were no specific criteria for the offense.

In some cases, transgender women said police arrested them because they had a "soft voice" or "smooth skin."

HRW said it found several cases in which police officers took advantage of the law to blackmail transgender women into sex. Transgender women claimed police used the threat of arrest to force them into sex, and sexual abuse at the hands of the police has been rampant.

"No one - regardless of his or her gender identity - deserves to be arrested on the basis of a vague, arbitrary law and then abused and tortured by police," said Sarah Leah Whitson, Middle East director at HRW.

"The Kuwaiti government has a duty to protect all of its residents, including groups who face popular disapproval, from brutal police behaviour and the application of an unfair law."

HRW also said transgender women reported suffering abuse by police while in detention, including being forced to strip and parade around the police station, and having to dance for officers.

"The Kuwaiti authorities should ensure proper monitoring of police behaviour," Whitson said.

"They should also investigate unchecked police abuse, hold those found guilty accountable for their actions, and make sure that vulnerable populations, such as transgenders, have access to mechanisms of redress without fear of retribution."

Transgender people in Gulf countries remain largely anonymous, as they could face heavy fines or jail sentences for dressing or acting like the opposite sex.

Kuwait, one of the richest countries in the world thanks to its oil wealth and small population, has seen protests in recent months for democratic reforms and nationality rights for thousands of non-citizens.