Russian investigators have cracked a ring of human traffickers that specialised in selling babies in the country's volatile North Caucasus region, Moscow's Investigative Committee said on Thursday.

Police detained a 62-year-old woman in the regional capital of Chechnya when she tried to sell a newborn baby boy for 550,000 roubles ($17,500) to an undercover policeman posing as a potential client.

The pensioner had also sold an 18-month-old girl to another undercover policeman earlier this year, the Investigative Committee said in a statement on its website.

Investigators said they had detained a midwife in the neighbouring region of Dagestan in relation to the case.

"Investigators are establishing other possible participants in the crime ring," said the statement from the committee, a government agency that handles criminal investigations.

Moscow has patchy control over the North Caucasus, where Muslim militants are fighting an insurgency aimed at creating an Islamic state in the predominantly Muslim territory.

The epicentre of daily violence has shifted from Chechnya, where militants fought two separatist wars against Russian troops, to Dagestan, a region wracked by inter-ethnic grievances where residents complain of neglect and poor services.

An unnamed law enforcement official told Interfax news agency the 62-year-old woman had received the baby boy from other members of the trafficking ring, brought him to Chechnya and tried to seal the transaction in the "Yellow Sea Cafe".

Russian media said the ring was made up of 12 people, some of whom worked in a hospital in Dagestan and procured babies to sell to Russians and foreigners.

Human rights groups accuse the authorities in a number of the North Caucasus regions - stretching from the Black Sea to the Caspian Sea - of rights abuses committed in the name of clamping down on the Islamist insurgency. ($1 = 31.3565 Russian roubles)