Moscow - Russian explorers dived deep below the North Pole in a submersible on Thursday and planted a national flag on the seabed to stake a symbolic claim to the energy riches of the Arctic.

A Russian miniature submarine is seen under water in the Arctic Ocean in this Reuters Television image taken from a television broadcast, August 2, 2007. [Reuters]

A mechanical arm dropped a specially made rust-proof titanium flag onto the Arctic seabed at a depth of 4,261 meters under the surface, Itar-Tass news agency quoted expedition officials as saying.

Russia wants to extend right up to the North Pole the territory it controls in the Arctic, believed to hold vast reserves of untapped oil and natural gas.

Under international law, the five states with territory inside the Arctic Circle -- Canada, Norway, Russia, the United States and Denmark via its control of Greenland -- have a 320 km economic zone around the north of their coastline.

But Russia is claiming a larger slice extending as far as the pole because, Moscow says, the Arctic seabed and Siberia are linked by one continental shelf.

"Then Russia can give foundation to its claim to more than a million square kilometers of the oceanic shelf," said a newsreader for Russia's state news channel Vesti-24, which made the expedition their top news story.

"It was a soft landing," Tass quoted expedition leader Artur Chilingarov as saying from on board one of the submersibles.

The rest of the expedition team, floating on a support vessel between the giant ice sheets of the Arctic, broke into applause when news came through the mission had been completed.

"There is yellowish gravel down here. No creatures of the deep are visible," said Chilingarov, 67, a veteran Arctic explorer and parliament deputy for the pro-Kremlin party.

Arctic Adventure

Expedition leaders have said their main worry is to resurface at the ice hole where they dived as the mini-submersibles are not strong enough to break through the North Pole's desolate ice cap.

One of the aims of the expedition is to allow oceanographers to study the seabed and establish that Russia and the North Pole are part of the same shelf.

"The aim of this expedition is not to stake Russia's claim but to show that our shelf reaches to the North Pole," Foreign Minister Sergei Lavrov told reporters in Manila, where he is attending a regional security conference.

The Mir-1 submersible reached the seabed at 1208 Moscow time (4:08 am EDT).

A second Russian submersible, manned by Swedish businessman Frederik Paulsen and Australian adventurer Mike McDowell, reached the seabed 27 minutes later. It reached a depth of 4,302 meters.

Soviet and US nuclear submarines have often traveled under the polar icecap, but no one has so far reached the seabed under the Pole, where depths exceed 4,000 meters.

The seabed of the Arctic is suspected to contain vast resources of natural gas, one of Russia's biggest exports, said Chris Weafer, chief strategist at Alfa Bank in Moscow.

"The exploration that has taken place in the Arctic over the past 15 years, made possible because of the receding ice cap, has given very positive indications of substantial structures, particularly natural gas structures," Weafer said.