The Memorial organisation said in the appeal that most violations in the predominantly Muslim North Caucasus region involve people who were snatched from their homes for ransom by the local police.

“We are forced to note that there has been no improvement in the absolute lawlessness and severe violations of human rights in Chechnya,” Interfax quoted the letter to Medvedev as saying.

The head of Russia’s main anti-torture organisation separately told reporters that “every case” brought to the group’s attention by locals involved kidnappings by the police.

“The police take a person away, he vanishes, and then there is no more information,” Interfax quoted Igor Klyapin as saying.

“Out of seven (recent) cases, the person only returned once,” he said.

Memorial was forced to close its office in Chechnya in the summer of 2009 after the unsolved murder of the campaigner Natalya Estemirova, which the group blames on local authorities.

But the organisation still sends field missions to the restless regions, which after two brutal civil wars is being governed by a Kremlin-appointed leader who is accused of mass human rights violations.

Much of the violence has spilled in recent years from Chechnya to the neighbouring republics of Ingushetia and Dagestan, with the latter experiencing almost daily bombings and killings.