An expedition aimed at strengthening Russia's claim to much of the Arctic Ocean region reached the North Pole on Wednesday afternoon and immediately began preparations for unloading two mini-submarines that will mark the sea floor with a capsule carrying a Russian flag.

The Rossiya atomic icebreaker had plowed a path to the pole through a sheet of multiyear ice, clearing the way for the Akademik Fedorov research ship to follow, said Sergei Balyasnikov a spokesman for the Arctic and Antarctic research institute that prepared the expedition.

The voyage, led by polar explorer and Russian legislator Artur Chilingarov, has some scientific goals, including the study of Arctic plants and animals. But its chief aim appears to be to advance Russia's political and economic influence by strengthening its legal claims to the gas and oil deposits thought to lie beneath the Arctic sea floor.

"I think that one of the tasks, at least for public consumption, is to put a claim and enlarge our territory by achieving the recognition of the Arctic shelf as a continuation of Russia's Eurasian part," Sergei Pryamikov, director of the international department of the St. Petersburg-based institute, told Russia's RTR Television.

In the coming hours, Russian scientists at the pole hope to dive in two mini-submarines to a depth of more than 13,200 feet, and drop a metal capsule carrying the Russian flag onto the sea bed. Balyasnikov said the dive was expected to start Thursday morning and last several hours. Each submarine will carry three people.

"For the first time in history, people will go down to the sea bed under the North Pole," Balyasnikov told The Associated Press. "It's like putting a flag on the moon."

The symbolic gesture, along with geologic data being gathered by expedition scientists, is intended to prop up Moscow's claims to more than 460,000 square miles of the Arctic shelf — which, by some estimates, may contain 10 billion tons of oil and gas deposits.

The expedition reflects an intense rivalry between Russia, the United States, Canada and other nations whose shores face the polar ocean for the Arctic's icebound riches.

The U.S. State Department noted that Russia has not yet made public the research allegedly backing its position and said the best available scientific evidence suggests the ridges in question are oceanic by nature "and thus not part of any country's continental shelf."

"While the United States remains skeptical, we have not had the opportunity to examine any of the recently obtained data," said Leslie Phillips, a department spokeswoman. "We wish the Russian scientists a safe expedition."

Moscow has claimed the polar region since at least the days of the Bolsheviks. It argued in 2002, in an application to the United Nations committee that administers the Law of the Sea, that geological data backed up this claim.

The U.N. rejected Moscow's application, citing lack of evidence, but Russia is set to resubmit it in 2009.

The U.S. Senate has not yet ratified U.S. accession to the Law of the Sea, which would give Washington a seat on the panel that will consider and eventually rule on the Russian claim.

Phillips said the Bush administration would continue to press hard for ratification in order to give the United States a voice on the commission.

"The Russians were asking to claim 45 percent of the area of the Arctic Ocean," George Newton, former head of U.S. Arctic Research Commission, said on WAMU 88.5, the leading public radio station for NPR news and information in the greater Washington, D.C., area. "That's significant. With this ability now to mount a more aggressive research program Russia has made efforts to confirm or get additional data that will enable them to resubmit the claim."

About 100 scientists aboard the Akademik Fedorov are specifically looking for evidence that the Lomonosov Ridge — a 1,240-mile underwater mountain range that crosses the polar region — is a geologic extension of Russia, and therefore can be claimed by it under the U.N. Convention on the Law of the Sea.

The subs will collect specimens of Arctic plants and animals and videotape the dives.

The biggest challenge, scientists say, will be for the mini-sub crews to return to their original point of departure to avoid being trapped under a thick crust of ice. "They have all the necessary navigation equipment to ensure safety," Balyasnikov said.

Newton, who served 25 years in the U.S. Navy as a submarine officer, said the Russian mini-subs will face dangers, such as a possible change in weather.

"The character of the ocean surface, the ice that is on the ocean surface can change dramatically, a storm can arise," Newton told WAMU. "It's not a trivial effort."

Denmark hopes to prove that the Lomonosov Ridge is an extension of the Danish territory of Greenland, not Russia. Canada, meanwhile, plans to spend US$7 billion (euro5.11 billion) to build and operate up to eight Arctic patrol ships in a bid to help protect its sovereignty.

The U.S. Congress is considering an US$8.7 billion (euro6.35 billion) budget reauthorization bill for the U.S. Coast Guard that includes US$100 million (euro72.96 million) to operate and maintain the nation's three existing polar icebreakers. The bill also authorizes the Coast Guard to construct two new vessels.

A senior Russian lawmaker said Wednesday that Moscow also needs to bolster its military forces in the region.

Russia "will have to actively defend its interests in the Arctic," Andrei Kokoshin said, according to the Interfax news agency. "There is something to think about on the military side, as well. We need to reinforce our Northern Fleet and our border guards and build airfields so that we can ensure full control over the situation."