Transneft, the state pipeline monopoly, is proposing to build the $11 billion (£6.3 billion) pipeline from Eastern Siberia to the Pacific Coast, via the Chinese border, to supply oil-thirsty Asian markets.

The proposed route comes within 800m of Baikal, a Russian national treasure and a Unesco World Heritage Site that contains 20 per cent of the world’s unfrozen fresh water. Environmental activists said that they would fight the decision in the courts and organise protests in defence of Baikal, which is home to hundreds of species and revered by local ethnic minorities.

A panel of experts from Rostekhnadzor, the environmental watchdog, overwhelmingly rejected the plan last month on the ground that Baikal could be irreparably damaged if the pipeline ruptured.

Out of 52 experts on the commission, 46 ruled that there were insufficient safeguards to protect the pipeline from the region’s frequent and powerful earthquakes. But Konstantin Pulikovsky, the head of Rostekhnadzor, refused to endorse the decision and appointed an extra 34 people to the commission, which then approved the project on March 3.

Opponents of the plan accused him of excluding scientists who were against the project and adding others who supported it, to get the necessary two-thirds majority.

Gennady Chegasov, a member of the commission, said that other panel members had been threatened with losing their jobs — a tactic that he said would have been unusual even in the Soviet era. “The unprecedented amount of boorishness and pressure would not be possible without the Government’s support,” he said. “I am prepared to appear as an expert and as a witness of the violations that took place.”

Greenpeace is appealing to American, European and Japanese banks to refuse to finance the project. Roman Vazhenkov, Greenpeace campaign co-ordinator, said: “This decision once again demonstrates that private interests of a group of oil industry officials . . . have more weight than the law, opinions of scientists and Russian citizens, and than the future of the world’s most unique freshwater lake.”

But analysts say that the project is certain to go ahead since President Putin has personally approved it and last year accused its opponents of hampering Russia’s development.

The Natural Resources Ministry turned down the proposed route in September but reversed its decision two months later under what was widely seen as pressure from the Kremlin.

Transneft expects to start building the pipeline in May, when the Government is likely to give its final approval to the project. It says that changing the route would unnecessarily delay construction and add hundreds of millions of dollars to the cost of the project.

Simon Vainshtok, Transneft’s president, promised in an interview last month that the pipeline would be three times the usual thickness around Baikal to ensure that there were no leaks.

“Transneft will take all the requisite precautions for Baikal to stay safe,” he told the government newspaper, Rossiyskaya Gazeta.

He also said that Greenpeace and other environmental groups were being manipulated by “puppet masters” outside Russia, who did not want China to grow in strength by importing more Russian oil.

Transneft says that the pipeline will be completed within three years and will pump up to 1.6 million barrels a day to China and the Pacific coast. Most environmental activists say that they do not object to the pipeline, only its proposed route.

“Even if billions of dollars are at stake, the Russian Government cannot put Lake Baikal at risk,” said Andrei Poyarkov, a member of the expert panel and a biologist at the Institute of Ecology and Evolution in the Russian Academy of Sciences. “They do not have the right.”

WORLD'S DEEPEST AND OLDEST LAKE

Lake Baikal was designated a Unesco World Heritage Site 10 years ago

Deepest (1,700m) and oldest (25 million years) freshwater lake; contains nearly 20 per cent of the world’s unfrozen fresh water

Holds more endemic species of plants and animals than any other lake

Home to the world’s only freshwater seals. Fish include salmon, sturgeon, burbot, oilfish, bullhead, grayling and omul

Contains more than 1,000 species of aquatic flora, including 20 flowering plants

The surrounding forests are home to many animals, including bears, elk, lynx, and sable

The lake’s origin continues to be debated; one theory says that it is a result of the Earth’s crust slowly subsiding

The soil in the lake has increased by two and half times over the past century because of agricultural and industrial development