Human rights group Amnesty International said Sunday it had "credible evidence" of the abuse and torture of people detained in sweeping arrests since Turkey's July 15 coup attempt.
The London-based group claimed some of those being held were being "subjected to beatings and torture, including rape, in official and unofficial detention centres in the country".
In Turkey, a senior official denied Amnesty's claims and vowed that Turkey would uphold human rights.
"The idea that Turkey, a country seeking European Union membership, would not respect the law is absurd," the official said.
"We categorically deny the allegations and encourage advocacy groups to provide an unbiased account of the legal steps that are being taken against people who murdered nearly 250 civilians in cold blood."
Since the failed coup, a total of 13,165 people have been detained, President Recep Tayyip Erdogan said late Saturday.
This included 8,838 soldiers, 2,101 judges and prosecutors, 1,485 police officers and 689 civilians.
At least 123 generals and admirals have also been jailed, Turkish Prime Minister Binali Yildirim said.
Amnesty said it had received reports that police in the capital Ankara and Istanbul were holding detainees in "stress positions" for up to 48 hours.
It claimed detainees were also being denied food, water and medical treatment while being verbally abused and threatened.
Two lawyers in Ankara working on behalf of detainees had told Amnesty that detainees had told them they saw senior military officers being raped.
Amnesty said that higher-ranking military officials were subject to worse treatment in comparison with other detainees.
It said its report was based on interviews conducted with lawyers, doctors and one person on duty in a detention facility.
The suggestion from one interviewee was that torture was used so that "they (detainees) would talk".
A lawyer at Istanbul's Caglayan courthouse described how she saw one detainee try to throw himself out of a sixth storey window, Amnesty said.
"Turkey is understandably concerned with public security at the moment, but no circumstances can ever justify torture and other ill-treatment or arbitrary detention," said Amnesty's Europe director John Dalhuisen.
He urged the Turkish authorities to stop "these abhorrent practices" and allow international monitors into the centres where detainees are held.afp