In a report obtained Monday by The Associated Press, the United Nations Environment Program says government assessments do not take into account the effects the various projects will have on the region's unique wildlife.
The report is to be published Tuesday and is based on the U.N. program's three-day trip to Sochi in January.
Russia's dated Black Sea resort of Sochi is under the spotlight as the next Winter Olympics host. As constructors set about building all facilities from scratch, environmental activists say the ecosystems have already sustained irreversible damage and bird and bear habitats have been destroyed. The government says it is aware of the concerns and accuses the activists of trying to sabotage the games as a public relations stunt.
The Sochi Games are a pet project of Prime Minister Vladimir Putin, who broke tradition to deliver a speech in English to the International Olympic Committee in 2007 during the bidding stage. Putin's spokesman, Dmitry Peskov, declined immediate comment, saying he hadn't seen the UNEP report.
The "Sochi 2014 Report of the UNEP 2nd Expert Mission" was based on the body's three-day trip to Sochi in January, which involved visits to various sites considered sensitive along the construction path of a combined road and rail link that connects a coastal facilities with a mountain facilities.
The World Wildlife Fund and Greenpeace Russia say the chief environmental threat is to the Mzymta River, which the communications link is set to follow. Thousands of beech trees have been felled to clear the path for the link.
UNEP also said Sochi organizers were delaying political decisions that would mitigate and compensate for the environmental fallout of the games.
"The mission observed that decisions taken at the political level ... are taking too long," the report said. The report cited such projects as the enlargement of Sochi National Park, better protection of the Mzymta valley, and the creation of new protected areas along the Black Sea coast that would host migratory birds.
The WWF and Greenpeace recently suspended their co-operation as consultants for Olympstroi, the state-run constructor, in protest that their concerns were being ignored.
The UNEP report urged both the activists and the government to continue cooperating, saying there was a "reluctance to engage with or even listen to each other's calls for actions from both sides."
The UNEP recommended a "comprehensive assessment of the overall impact of the Olympic and tourism projects on the ecosystem." UNEP added that the activists' concerns sparked the decision to visit Sochi and produce a report.
The Sochi Games are adopting a unique "cluster" strategy. A coastal cluster of arenas will host skating sports, and a mountain cluster will handle skiing, snowboard and other events.