Beatings with bottles, sleep deprivation and threats of violence against relatives are all routine forms of torture in detention centres in the rebellious Russian region of Chechnya, former inmates say.

Though Russian government officials deny systematic abuse of prisoners, rights groups say abuse is frequent in Chechnya, where rebels have fought Moscow's rule for 15 years.

Chechens detained on suspicion of backing the rebels say they will never recover from their experiences, above all at a notorious facility in the regional capital Grozny that even Russia's Chechen allies have demanded be closed.

Housed in a four-storey grey building guarded by towers with machinegun nests and a grey concrete fence, "Operational Investigation Bureau No. 2", or ORB-2, comes under the direct authority of the Russian Interior Ministry.

"The cell walls were smeared with blood, they chained me to a hot radiator. Then they started to conduct inhuman tortures. The same demands over and over," Ali Techiyev, a 21-year-old accused of fighting against Russia, said in a written statement recently made available to Reuters.

"They beat me with a sand-filled bottle over the head, the feet, the kidneys and other parts of my body. The torturers changed over every night. They got tired beating me," he said.

Techiyev's statement, addressed to local officials, said he was regularly taken from detention to ORB-2 for interrogation. He had tried to appeal to the courts without success.

"My torturers say they take their orders only from Moscow, and that no one can help me," said Techiyev, who remains in detention. He passed the statement to relatives during a visit.

Abusaid Azimov told Reuters his brother Anzor was taken to OBR-2 earlier this year and also accused of fighting Russia.

"The torture went on day and night for three days. Then they said if he didn't admit his guilt they would bring in his relatives and beat us until he signed," Abusaid said.

ACCESS DENIED

The International Committee of the Red Cross (ICRC), which monitors treaties on prisoner rights, ended its Chechen visiting program in May, saying officials did not allow full access.

The ICRC appealed to Russian President Vladimir Putin in June for help with restarting the visits, but a spokeswoman said on Wednesday that no progress had been made.

In May, journalists managed to visit a former detention center before it was demolished. Its three cells were small and filthy, and inmates' graffiti on the walls talked of suffering.

"(Police) you'll pay for what you've done to us. We will get our revenge, Allah willing," said one inscription.

"Where am I? What is happening? Am I alive?" said another.

The number of detainees in the Chechen centers is not known, but hundreds of Chechens have been convicted of fighting Russia and sentenced to long prison terms, often in Russia's remote Arctic region, far from their southern home.

Local and international rights groups, who have long argued that these men face torture to extract confessions, won an unlikely ally in April when warlord Ramzan Kadyrov, who heads Chechnya's Moscow-backed government, said OBR-2 should be closed because it "massively breaks the law".

"The problems of kidnap and disappearances, of torture of people detained in the Chechen Republic ... are not being solved," said rights group Memorial after Kadyrov spoke.