The Baltic is said to be one of the world's most polluted seas

Russian Prime Minister Vladimir Putin has defended his country's Nord Stream gas pipeline against accusations that it will damage the fragile Baltic Sea.

He said extensive research had been carried out on the environmental impact and that the project would be "safe".

He was speaking in Helsinki at a summit of leaders from Baltic countries.

The Baltic is already a sink for chemical pollutants and untreated sewage, and is said to be one of world's most polluted seas.

Weapons on seabed

Construction of the Nord Stream pipeline is due to begin this year, with completion set for 2012.

It is meant to pump 55bn cubic metres of gas per year from Russia directly to Germany.

"I believe that Nord Stream will be environmentally safe and reliable, and a very good supplier of natural gas to Europe and make our continent more stable," Mr Putin said.

He said more than 100m euros had been spent on environmental research and expressed surprise at the "emotional response" of critics.

Other Baltic countries fear the project could stir up toxins lying on the sea bed, especially those inside a vast number of WWII-era armaments.

"It's serious. We are worried about the dioxins and other poisons on the seabed," Estonian Prime Minister Andrus Ansip said.

"We expect our scientists to get full information about it all."

Three years ago the nine countries with a Baltic coastline set the goal of restoring the sea to health by 2021.

Finnish President Tarja Halonen urged leaders of the nine countries to speed up their action.

"Today, some of the richest and most environmentally conscious countries on Earth live on the shores of one of the world's most polluted seas," she said.

"Isn't it a tragedy?"