MOSCOW — Russian scientists hope to plunge to the seabed beneath the North Pole in the next few days in a miniature sub and plant a titanium capsule containing the Russian flag, symbolically claiming much of the Arctic Ocean floor for Moscow.

Thick sea ice threatens to thwart the expedition, an engineer with Russia's premier polar research institute said Friday. But if the effort succeeds, it could mark the official start of a very cold diplomatic war for the Arctic, one of the Earth's last energy frontiers.

A convoy consisting of a research vessel and an icebreaker, and led by Russia's most famous polar explorer, set sail Tuesday from Murmansk toward the North Pole — shadowed, according to Russian TV reports, by at least one Norwegian military aircraft.

On Saturday, Russian researchers expect to perform test dives to depths of more than a mile in two miniature subs near Franz Josef Land, a Russian archipelago in the Arctic Ocean.

The expedition, supported by the Kremlin, was dispatched to buttress Russia's claims to more than 460,000 square miles of the Arctic shelf — an area that by some estimates contains 10 billion tons of oil and gas deposits. Experts say the effort is part of Russia's long-range efforts to expand its energy empire.

Arkady Soshnikov, chief engineer of Russia's Arctic and Antarctic Scientific Research Institute in St. Petersburg, told The Associated Press this year's unusually thick sea ice could hamper the expedition.

While the nuclear-powered icebreaker Rossiya is capable of pushing through most pack ice, Soshnikov said, the research vessel Akademik Fyodorov may have trouble following. Still, the current plan calls for the mini-subs to descend to the seabed under the North Pole on Monday or Tuesday, he said.

Despite this summer's conditions near the pole, the area of the Arctic Ocean covered by ice has been shrinking since the early 20th century and the change has accelerated in the last decade, according to the U.S. National Oceanic and Atmospheric Administration. Some scientists blame the shrinkage on the effects of human-driven climate change.

As the Arctic's ice recedes, its waters are becoming more navigable — and its riches more accessible to a resource-hungry world.

The largely unexplored Arctic seabed could contain vast oil and gas deposits; the recoverable petroleum reserves of several countries that claim the shores of the northern polar ocean — including the U.S., Russia and Norway — are rapidly being exhausted.