German environmentalist groups said Wednesday they have filed suit to block construction of the Nord Stream gas pipeline through the Baltic Sea from Russia to Germany.

The challenge, which could hold up the energy project, was filed with the administration tribunal in the Baltic city of Greifswald by WWF and the German affiliate of Friends of the Earth, BUND.

Nord Stream, a consortium led by Gazprom of Russia, has already received much of the steel pipe for the line.

The environmentalists are challenging a permit to dig up the seabed under German territorial waters and place the pipes in this trench. They said the Office of Mines, which issued the permit, had not insisted on enough repairs to the ecosystem after the work.

The environmentalists said excavating the mud would release nitrogen and phosphorus into the water, threatening marine life.

They demanded that an agreed cash penalty of 7 million euros (10 million dollars) to be paid by Nord Stream be entirely spent on repairing the damage. Nord Stream aims to start laying the 7.5-billion-euro pipeline in April and start pumping in late 2011.

Copyright 2010 dpa Deutsche Presse-Agentur GmbH