Decisions by Sweden and Finland to allow the Russian-led Nord Stream pipeline to pass through their waters has unleashed strong reactions in both countries, with political parties and media contending that Russian pressure overpowered environmental concerns.

"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 7.4-billion-dollar (5.0-billion-euro) 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 1,220 kilometres (758 miles), 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.

Shortly after Sweden's approval on Thursday, the Left and Green parties, as well as the country's Greenpeace group, also condemned the move.

"The most environmentally-friendly alternative was to run the pipeline next to the existing passage on land. But Nord Stream did not bother to investigate that," Greenpeace said in a statement Thursday.

Green Party spokesman Peter Eriksson said the pipeline would cause "great damages" to the Baltic Sea.

As the country that holds the EU presidency, "Sweden's government talked about the importance of protecting the Baltic Sea, but (the decision) shows it did not mean" what it said, he told Swedish television Thursday.

In Finland, an editorial in the country's largest broadsheet Helsingin Sanomat on Friday said the government should have imposed stricter conditions on environmental conditions before approving the project.

"Finland could have put more pressure" on Russia to sign a treaty respecting environmental conditions, it argued.

In another opinion piece in the same paper, Pertti Joenniemi, an expert at the Danish Institute for International Studies, said it was "clear that the Baltic Sea region cannot become ... a model for European development unless the (environment and security) fears related to pipeline project are cleared out of the way."

Although the Finnish government approved Nord Stream on Thursday, the Western Finland Environmental Permit Authority still needs to deliver the permit for building or installing the pipeline.

"We will make a decision (on Nord Stream's building permit) at the earliest at the end of this year, but it might be in early next year," Mika Seppaelae of the Western Finland Environmental Permit Authority told AFP.

The approvals came as new tensions have emerged between Russia and Ukraine, raising fears for a new row between the countries that could jeopardise Russian gas supplies to Europe.

By going under the Baltic Sea, Nord Stream's pipeline could free the European Union of the risks posed by disputes between Russia and Ukraine, through which 80 percent of Russian gas currently transits on its way to Europe.

One quarter of all gas consumed in Europe comes from Russia.