Russian authorities have transferred a leading critic of the environmental cost of the Sochi Olympics to a penal colony after ordering him to serve a three-year prison term, his group said Monday.

Environmental campaigner Yevgeny Vitishko was ordered during the Winter Olympic Games to serve what had been a suspended three-year sentence, in a verdict that alarmed rights groups.

After that judgement, Vitishko was held in a detention centre in Krasnodar, the capital of the region that includes Sochi.

However, he has now been transferred from the region to serve his sentence in line with the court ruling, his group Ecological Watch on the Northern Caucasus (EWNC) said in a statement.

"Vitishko has been taken out of the Krasnodar region and sent to a prison camp to serve his term," it said.

The group said Russia's prison service had not given any information over where he had been sent. It is usual practice in Russia for the authorities to give no information about the location of convicts until several days after they have arrived.

He could in theory have been sent to any of Russia's vast network of prison colonies. Such transfers are often made by train and can take many days.

Vitishko was convicted in 2012 of damaging a fence during a protest against the construction of what activists believe is a mansion for the region's governor in a public forest.

He received a three-year suspended sentence, but he was ordered on February 12 to serve that term in a penal colony after breaking the terms of the original sentence.

The International Olympic Committee said during the Games it was seeking a clarification from the Russian authorities but then said it had been assured the judgement was not Games-related.

Rights groups countered that the case has everything to do with the Sochi Games that wrapped up on Sunday, saying Russia was trying to muzzle one of the leading critics of the project spearheaded by President Vladimir Putin.

Vitishko and the EWNC have repeatedly highlighted the damage of the Games construction on what was once a pristine environment.

In a separate development, the EWNC said that two of its activists, Olga Noskovets and David Khakim, were arrested in the Matsesta district of Sochi on Sunday, the same day as the Sochi Games' closing ceremony.

It said that they had spent the night in police detention and would appear in court on Tuesday on accusations of disobeying police orders.

The group dismissed the accusations as false but said it expected them to be ordered to serve 15 days of administrative detention.