Image caption The subs have started their third season of exploration at Lake Baikal

Russian-owned submersibles would be able to cap the oil leak in the Gulf of Mexico, the captain of one of the vessels has said.

The skipper was speaking as two of the subs - which can dive to 6,000m - started a campaign of exploration at the bottom of Lake Baikal in Siberia.

He added that there was still time for the subs to help BP with the disaster.

The subs are searching for gas hydrates - a potential alternative fuel source - on the bed of Baikal.

Yevgenii Chernyaev told BBC News that the problem had to be addressed at the highest level.

Two oval-shaped submersibles have recently started their third season of exploration in Baikal - the world's deepest lake.

Anatoly Sagalevich of Russia's Shirshov Institute of Oceanology, which owns the vessels, said that he had an informal conversation with a BP representative asking if Mirs would be able to help stop the leak.

But he said there was no official request and no real discussions about the matter.

A BP spokesman told BBC News that the company had not had any formal contact with the Russians.

"We've had over 120,000 people come up with ideas," he said in an e-mail.

"We are looking through all of these to see which are viable. If [the Russians] want to contact us (or may have done so through some other channel), we can evaulate their idea."

Oil has been leaking from a damaged well in the Gulf of Mexico since a BP-operated drilling platform, Deepwater Horizon, exploded and sank in April.

And though BP says it is now able to gather some 10,000 barrels of oil a day, using a device that siphons oil up to surface ships, thousands of barrels of oil continue to gush daily from the ocean floor.

The US administration has already called the leak the biggest environmental catastrophe in the country's history.

Mr Chernyaev said that his team had held numerous discussions about the oil spill in the Gulf and the Russians would be ready to come to the rescue - but only if everything was done properly.

Image caption The subs have discovered reserves of gas hydrates on the bottom of the lake

Standing on a barge that transports the two subs after their submersion, the Mir-2 captain underlined that the subs were probably the only deep-sea vessels in the world capable of stopping the leak.

"Our subs are unique. There are two of them and they can submerge and work simultaneously. Also, they are powerful enough to work with any other additional equipment.

"There are only four vessels in the world that can go down to 6,000m - the Mirs, French Nautile and Japanese Shinkai. The Mirs are known to be the best, and we have a very experienced team of specialists," he said.

But Mr Chernyaev added that such an operation would have a chance of succeeding only if BP or the US government asked the Russian government to join efforts to stop the leak.

Image caption Mr Chernyaev said the problem had to be addressed at the highest level

"It should all be decided on the government level. Asking [Anatoly] Sagalevich [of Russia's Shirshov Institute of Oceanology, which owns the subs] to simply bring the Mirs over is nonsense. Even though we're able to go to much greater depths than where the damaged well is located, we wouldn't be able to do much on our own.

"We need a team of international specialists and we have to know all the details and probably even build a special device to attach to the subs, and all this needs time," said Mr Chernyaev.

He explained that the subs had already worked in much harsher conditions, such as the Arctic.

The submersible's pilot also said that the Russians were very surprised that BP and the US government had not asked them for help from the beginning.

"And we would not refuse to help, even though for us it would be very complicated, especially right now, when we're already working on Baikal. But it doesn't look like anyone seriously wants our help," he added.

Mr Chernyaev was one of the pilots on the first manned descent to the seabed under the geographic North Pole, carried out using the Mir mini-submarines. The expedition was widely reported as a bid to further Moscow's territorial claims in the Arctic.

Image caption The Mir submersibles can dive to a depth of about 6,000m

The two submersibles started their third season of exploration in Lake Baikal on 1 July. Over the last two expeditions, they found reserves of gas hydrates on the lake bed - which some consider a possible alternative fuel source of the future.

Gas hydrates are usually formed in permafrost or deep in the oceans. These are crystalline water-based solids; gases such as methane are trapped inside them within cages of hydrogen-bonded water molecules.

Baikal is the only freshwater basin where gas hydrates are found in its sediments. Scientists say the depth of the lake - reaching 1,637m - and extremely low temperatures of water near the lake bed both help gas hydrates form at depths exceeding 350m.

The current expedition aims to obtain important data about these findings, and is also searching for new life forms, which might be unique to Baikal.

Located in eastern Siberia, not far from the Mongolian border, the lake holds one-fifth of the planet's fresh water and many unique species of plants and animals, among them the nerpa - a species of freshwater seal.