AMSTERDAM (Reuters) - The Netherlands launched legal action against Russia to free Greenpeace activists charged with piracy after staging a protest at an offshore oil platform in the Arctic, the Dutch government said on Friday.

"The Netherlands today began an arbitration procedure on the basis of the (United Nations) Convention on the Law of the Sea," Frans Timmermans, foreign minister, wrote in a letter to parliament.

(Reporting By Thomas Escritt. Editing by Anthony Deutsch; Editing by John Stonestreet)