It is already the world's biggest country, spanning 11 time zones and stretching from Europe to the far east. But yesterday Russia signalled its intention to get even bigger by announcing an audacious plan to annex a vast 460,000 square mile chunk of the frozen and ice-encrusted Arctic.

According to Russian scientists, there is new evidence backing Russia's claim that its northern Arctic region is directly linked to the North Pole via an underwater shelf.

Under international law, no country owns the North Pole. Instead, the five surrounding Arctic states, Russia, the US, Canada, Norway and Denmark (via Greenland), are limited to a 200-mile economic zone around their coasts.

On Monday, however, a group of Russian geologists returned from a six-week voyage on a nuclear icebreaker. They had travelled to the Lomonosov ridge, an underwater shelf in Russia's remote and inhospitable eastern Arctic Ocean.

According to Russia's media, the geologists returned with the "sensational news" that the Lomonosov ridge was linked to Russian Federation territory, boosting Russia's claim over the oil-and-gas rich triangle. The territory contained 10bn tonnes of gas and oil deposits, the scientists said.

Russia's Komsomolskaya Pravda newspaper celebrated the discovery by printing a large map of the North Pole. It showed the new "addition" to Russia - the size of France, Germany and Italy combined - under a white, blue and red Russian flag.

Yesterday, however, some scientists doubted whether Russia's latest Arctic grab stood up to scrutiny.

To extend a zone, a state has to prove that the structure of the continental shelf is similar to the geological structure within its territory. Under the current UN convention on the laws of the sea, no country's shelf extends to the North Pole. Instead, the International Seabed Authority administers the area around the pole as an international area.

"Frankly I think it's a little bit strange," Sergey Priamikov, the international co-operation director of Russia's Arctic and Antarctic Research Institute in St Petersburg, told the Guardian. "Canada could make exactly the same claim. The Canadians could say that the Lomonosov ridge is part of the Canadian shelf, which means Russia should in fact belong to Canada, together with the whole of Eurasia."

Mr Priamikov said the area was one of breathtaking natural beauty. It was much drier, colder and quieter than the western Arctic, he added. "I've been there many times. It's an oasis for marine life," he said. Asked whether it would be feasible to drill for oil, he said: "Yes".

The shelf was 200 metres deep and oil and gas would be easy to extract, especially with ice melting because of global warming, he said.

Russia has the world's largest gas reserves. It is the second largest exporter of oil after Saudi Arabia. The Kremlin is keen to secure Russia's long-term hegemony over global energy markets, and to find new sources of fuel.

Russia first made a submission in 2001 to the UN commission on the limits of the continental shelf, seeking to push Russia's maritime borders beyond the existing 200-mile zone. It was rejected.

But the latest scientific findings are likely to prompt Russia to lodge another confident bid - and will alarm the US, which is mired in a 13-year debate over ratification of a UN treaty governing international maritime rights.

The Law of the Sea Treaty is the world's primary means of settling disputes over exploitation rights and navigational routes in international waters. Russia and 152 other countries have ratified it.

But the US has refused, arguing it gives too much power to the UN. If the US does not ratify it, Russia's bid for the Arctic's energy wealth will go unchallenged, proponents believe.