MOSCOW, Russia (AP) -- An expedition aimed at strengthening Russia's claim to much of the oil and gas wealth beneath the Arctic Ocean reached the North Pole on Wednesday, and preparations immediately began for two mini-submarines to drop a capsule containing a Russian flag to the sea floor.

The Rossiya icebreaker had plowed a path to the pole through an unbroken 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.

"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."

Russian scientists hope to dive in two mini-submarines beneath the pole to a depth of more than 13,200 feet, and drop a metal capsule containing the Russian flag on the sea bed.

Balyasnikov said the dive was expected to start Thursday morning and last for several hours.

The voyage, led by noted polar explorer and Russian legislator Artur Chilingarov, has some scientific goals, including the study of Arctic plants and animals. But its chief goal appears to be advancing 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.

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

About 100 scientists aboard the Akademik Fyodorov are 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 ice crust.

"They have all the necessary navigation equipment to ensure safety," Balyasnikov said.

Denmark hopes to prove that the Lomonosov Ridge is an extension of the Danish territory of Greenland, not Russia. Canada, meanwhile, plans to spend $7 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 $8.7 billion budget reauthorization bill for the U.S. Coast Guard that includes $72.96 million to operate and maintain the nation's three existing polar icebreakers. The bill also authorizes the Coast Guard to construct two new vessels.