A Russian expedition has proved that a ridge of mountains below the Arctic Ocean is part of Russia's continental shelf, government officials have said.
The Mir-I was used to help plant a Russian flag on the Arctic seabed
The Natural Resources Ministry said tests on soil samples showed Russia was linked to the Lomonosov Ridge.
Moscow has mounted several expeditions recently - and risked tensions with rivals in August by planting a flag in the seabed below the North Pole.
The Arctic is thought to be rich in oil, gas and mineral reserves.
Correspondents say Russia's main rivals for the supposed spoils - the US, Canada and Denmark - have been angered by Moscow's recent aggressive strategy in the region.
Under a United Nations convention, the country claiming ownership of the region's ocean floor must show evidence that the seabed is an extension of their continental shelf.
Moscow has repeatedly argued that the Lomonosov Ridge is part of its land mass - and now the Natural Resources Ministry believes it has the proof.
The ministry said analysis of samples from the ridge - taken in May and June - showed "the structure of the underwater Lomonosov mountain chain is similar to the world's other continental shelves".
Nasa photo shows ice cover in 2005 and as it was in 1979
The statement added: "The ridge is therefore part of Russia's land mass."
Marine research official Viktor Posyolov told Russia's Tass news agency the claim could extend Russia's seabed by 1.2m sq km (463,323 sq miles).
He said the territory could potentially yield 10,000 billion tonnes of conventional fuel.
In a further sign of its intent, the Kremlin announced that four strategic bombers were to make training flights over the Arctic and the Atlantic Ocean.
Russia's claim to a vast swathe of territory in the Arctic has sparked an increasingly tense rivalry with other countries who believe they have a claim.
After Russia planted its flag in the seabed, Canada vowed to increase its icebreaker fleet and build two new military facilities in the Arctic.
Denmark recently sent a team of scientists to the Arctic ice pack to seek evidence that the Lomonosov Ridge was attached to the Danish territory of Greenland.
And a US Coast Guard icebreaker also set off late last month for a research expedition - although scientists said the trip had been planned well before the Russian move.
Competition for territorial and economic rights has heated up as melting polar ice caps have introduced the possibility of exploiting the previously inaccessible seabed.
1) North Pole:
Russia leaves its flag on the seabed, 4,000m (13,100ft) beneath the surface
2) Lomonosov Ridge:
Russia argues that this underwater feature is an extension of its continental territory
3) 200-nautical mile (370km) line:
Shows how far countries' agreed
4) Russian-claimed territory:
The bid to claim a vast area is being closely watched by other countries