Researchers aboard two small Russian submarines have planted the country's flag nearly 4,300 meters below the North Pole.
The mission was aimed at laying claim to vast mineral riches below the polar ice cap.
After spending much of Thursday submerged in the Arctic Ocean, Russian television footage showed the two orange and white deepwater submarines surfacing through a giant hole cut in thick arctic ice.
Under international law, five countries hold territory inside the Arctic circle -- Canada, Norway, Russia, the United States, and Denmark, which controls Greenland. Russia is claiming an enlarged share extending to the North Pole, based on claims the Arctic seabed and Siberia are linked by a single submerged continental shelf.
Washington contends the Arctic ridges do not belong to any country's continental shelf, and that Arctic waters should remain open to international shipping.
Canada's foreign minister, Peter MacKay, dismissed the mission. He told CTV television "this isn't the 15th century. You can't go around the world and just plant flags and say 'We're claiming this territory'."
Russian Foreign Minister Sergei Lavrov said today the expedition aimed to prove scientifically that Russia's continental shelf stretches to the North Pole. Russia is seeking sovereignty over 1.2 million square kilometers of the Arctic seabed, which geological experts believe is rich in natural gas and minerals.