Police in Russia's Sochi on Thursday briefly detained a prominent environmental activist critical of Olympic development in the city, accusing him of slandering a judge.

But the activist, Andrei Rudomakha, who coordinates the regional NGO Environmental Watch on North Caucasus (EWNC) , dismissed the case as a pressure tactic by the authorities, the latest in a series of incidents targeting the group ahead of the Winter Games in the Black Sea resort next February.

"It's a form of pressure before the Olympics," he told AFP as he sat in a Sochi police station after being stopped in the street. Rudomakha was released after about three hours, his NGO said.

The incident took place as sports officials presided over a high-profile "Sport and the Environment" conference organised by the International Olympic Committee and the UN Environmental Programme in the Olympic Park, a five-day event that went on with the glaring absence of Russia's main environmental organisations.

Rudomakha said that he was clearly followed and possibly wiretapped by police before they stopped him on a Sochi street and told him to come to the station.

"They showed me a document from an investigator in Krasnodar ordering them to deliver me as part of a slander case," he said.

Last year Rudomakha, who also is the coordinator of the liberal Yabloko party in the southern Krasnodar region, was quoted in a party press release as saying a local judge acted "lawlessly" when arresting a fellow activist for 15 days after a protest.

But he said he had never received an official summons from investigators and seemed unsure of what will happen next.

The charge of slandering a judge can be punished by a fine of two million rubles ($62,000) or 360 hours of community service.

EWNC is highly critical of the development in Sochi ahead of the Olympic Games, particularly of the damage done to the Black Sea beaches as well as the Sochi National Park and the Caucasus Reserve, two protected territories in the mountains above the city.

A prior prosecution had already forced another EWNC activist active in Sochi inspections, Suren Gazaryan, to leave the country, while a third activist in Sochi was recently involved in a suspicious accident that landed him in a hospital for several days.

"I was breaking to let a truck make a turn, and my breaks weren't working," Vladimir Kimayev told AFP, adding that he saw a group of young men near his moped shortly before and suspects that they have meddled with the breaks.

"I have a feeling that the accident was provoked," he said, having just returned home from the hospital.

At the "Sport and the Environment" conference held at a luxury hotel near the Olympic venues, the IOC President Thomas Bach on Thursday said he was satisfied with the way Russian authorities were meeting environmental standards.

EWNC and Greenpeace Russia never received an invitation to attend the meeting. The World Wildlife Fund said they were invited but declined to participate due to their critical position over Sochi's Olympic development, spokeswoman Maria Vinokurova said.