"The pipeline is not in Sweden's interests, especially considering the project's far-reaching consequences on the environment," Social Democrat foreign affairs and environment critics Urban Ahlin and Anders Ygeman said in a open letter published in the Svenska Dagbladet newspaper.

"But it is undoubtedly in Russia's interests," they wrote, stressing the timing of the decision "suggests that the Swedish government has in a way" given into Russia's "expressions of of discontent." Sweden's approval came two weeks before a EU-Russia summit to take place in Stockholm and resolved what had become a dispute between Stockholm and Moscow.

After years of procrastination, Sweden and Finland gave breakthrough approvals to Nord Stream on Thursday, allowing the pipeline to pass through their waters in the Baltic Sea, a crucial step for the project destined to supply Europe with Russian gas.

Sweden currently holds the rotating EU presidency. In June, Russia's ambassador to the EU Vladimir Chijov asked the Swedish prime minister to make Nord Stream one of his presidency's priorities.

The US$7.4 billion Nord Stream project, which is led by Russian state-run energy giant Gazprom in partnership with Germany's E.On Ruhrgas and BASF-Wintershall, will run under the Baltic Sea to bring gas from Russia to the European Union.

The pipeline will link the Russian city of Vyborg and Greifswald in Germany over a distance of 1,220km, going under the Baltic Sea and passing through Russian, Finnish, Swedish, Danish and German waters.

"The approval of the pipeline permanently ties Europe to an addiction to Russian gas that involves serious environmental risks in a very sensitive sea area," the Social Democrat critics wrote.\