Detainees have been beaten, sexually abused and threatened with rape by Turkish police, Human Rights Watch has claimed.

In a 43-page report published on Tuesday, the human rights group said a "climate of fear" had prevailed since July's failed coup against President Tayyip Recep Erdogan and the arrest of thousands under a state of emergency.

It said Turkey had effectively written a "blank cheque" to security services to torture people.

Turkey's Justice Ministry has repeatedly denied prisoners are ill-treated and said a unit had been established to investigate all claims. Ankara said the post-coup crackdown was necessary to stabilise a Nato state facing threats from Kurdish militants as well as wars in neighbouring Iraq and Syria.

In pictures: Turkey coup attempt Show all 17 1 /17 In pictures: Turkey coup attempt In pictures: Turkey coup attempt Turkish President Erdogan attends the funeral service for victims of the thwarted coup in Istanbul at Fatih mosque on July 17, 2016 in Istanbul, Turkey Burak Kara/Getty Images In pictures: Turkey coup attempt Soldiers involved in the coup attempt surrender on Bosphorus bridge with their hands raised in Istanbul on 16 July, 2016 Gokhan Tan/Getty In pictures: Turkey coup attempt A civilian beats a soldier after troops involved in the coup surrendered on the Bosphorus Bridge in Istanbul, Turkey, 16 July, 2016 REUTERS/Murad Sezer In pictures: Turkey coup attempt Surrendered Turkish soldiers who were involved in the coup are beaten by a civilian Reuters In pictures: Turkey coup attempt Soliders involved in the coup attempt surrender on Bosphorus bridge Getty In pictures: Turkey coup attempt Supporters of Turkish President Recep Tayyip Erdogan wave flags as they capture a Turkish Army vehicle Getty In pictures: Turkey coup attempt People pose near a tank after troops involved in the coup surrendered on the Bosphorus Bridge in Istanbul, Turkey, 16 July, 2016 Reuters In pictures: Turkey coup attempt Turkish soldiers block Istanbul's Bosphorus Brigde Getty In pictures: Turkey coup attempt A Turkish military stands guard near the Taksim Square in Istanbul Reuters In pictures: Turkey coup attempt Pierre Crom/Twitter In pictures: Turkey coup attempt Turkish soldiers secure the area as supporters of Recep Tayyip Erdogan protest in Istanbul's Taksim square AP In pictures: Turkey coup attempt People demonstrate in front of the Republic Monument at the Taksim Square in Istanbul Murad Sezer/Reuters In pictures: Turkey coup attempt Turkish soldiers detain police officers during a security shutdown of the Bosphorus Bridge Reuters In pictures: Turkey coup attempt Turkish Army armoured personnel carriers in the main streets of Istanbul Getty In pictures: Turkey coup attempt Chaos reigned in Istanbul as tanks drove through the streets EPA/TOLGA BOZOGLU In pictures: Turkey coup attempt Turkish President Tayyip Erdogan speaks to media in the resort town of Marmaris Reuters In pictures: Turkey coup attempt Supporters of President Erdogan celebrate in Ankara following the suppression of the attempted coup Reuters

HRW said it had uncovered 13 alleged abuse cases, ranging from the use of stress positions and sleep deprivation to severe beatings, sexual abuse and the threat of rape. The cases were not limited to possible supporters of the coup but also included detainees suspected of links to Kurdish militant and leftist groups.

Hugh Williamson, Europe and Central Asia director at HRW, said in a statement it "would be tragic if two hastily passed emergency decrees end up undermining the progress Turkey made to combat torture."

"By removing safeguards against torture, the Turkish government effectively wrote a blank cheque to law enforcement agencies to torture and mistreat detainees as they like," he said.

Turkey has arrested more than 35,000 people following the coup, detained thousands more and sacked over 100,000 over their suspected links to Fethullah Gulen, a US-based cleric Mr Erdogan blames for orchestrating the coup. Mr Gulen denies the charge.

Turkey's President Erdogan defends government action

The government has said the widescale crackdown is justified by the gravity of the threat to the state on 15 July, when rogue soldiers commandeered tanks and fighter jets, bombed the country's parliament and killed more than 240 people.

Mr Erdogan declared a state of emergency days after the failed putch, allowing him and the cabinet to bypass parliament in enacting new laws and to limit or suspend rights and freedoms as deemed necessary.

Emergency decrees have since extended the period of police detention without judicial review from four days to 30, and have allowed the authorities to deny detainees access to lawyers for up to five days, and restrict their choice of lawyer.

Eight of the cases reported to HRW took place in the immediate aftermath of the coup, before the emergency decrees were published, while five took place after they were adopted.

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In one, a lawyer told HRW several detainees had been forced to undress and left out in the baking sun for hours. She said the police then severely beat them and threatened to rape them with a baton.

In a statement to the prosecutor seen by HRW, one detainee described how he was blindfolded and then beaten by police. “The police chief who detained me… began to slap me in the face and eyes,” he said. “They beat me on the soles of my feet, on my stomach, then squeezed my testicles, saying things like they’d castrate me.” He went on to describe a series of beatings on other parts of his body.

It also quoted one police officer telling a detainee: "Because of the state of emergency, nobody will care if I kill you. I will just say I shot you while you tried to run away." It said those words were overheard by the relative of another person in detention.

HRW called on the authorities to "immediately rescind those provisions of the emergency decrees that enable abuse".

People kick and beat a Turkish soldier, who participated in the attempted coup, on Istanbul's Bosphorus Bridge (AP)

It said the government has "the right – and even the obligation – to protect the public, investigate crimes committed during the attempted coup, including murder and causing bodily harm, and to hold those responsible to account.

"However, declaring a state of emergency does not give the government a carte blanche to suspend rights."

Amnesty International previously said it had received credible evidence of detainees being subjected to beatings, torture and rape in the immediate aftermath of the failed coup.