"The central mass media are quiet about this story," Marina Rikhvanova, co-chair of the International Socio-Ecological Union, said at a news conference.

"This is worrisome to everyone," she said.

Rikhvanova and four other environmental experts and local activists said Russia's main state broadcast media gave virtually no coverage to a rally last month in the Siberian city of Irkutsk to protest the planned pipeline, although it was covered by media elsewhere in Europe.

The protest drew more than 5,000 people and included public addresses against the pipeline project by key regional politicians, they said.

A representative of a local group called Baikal Is Not For Idiots complained of a "media boycott" of the controversy over plans by the state oil transport monopoly Transneft to build a strategic pipeline linking the fields of west Siberia to an outlet in Asia.

Environmentalists warn that the route for the pipeline reportedly favored by Transneft, skirting the lake's northern shores for dozens of kilometers, poses a major threat to the pristine environment of lake which is classified by the United Nations as a World Heritage Site.

In addition to regular pipeline malfunctions, the area around Lake Baikal is prone to earthquakes. A strong earthquake could rupture the planned high pressure pipeline and lead to massive spillage of crude oil into the lake, experts say.