The mission to the depths of Siberia's Lake Baikal is led by Artur Chilingarov, a scientist and Kremlin-backed member of parliament who was part of an earlier mission to the North Pole that sparked criticism in the West.

Tucked away in the remote hills of south-east Siberia where Russia borders China and Mongolia, Lake Baikal, the world's deepest and oldest lake, is home to some of the world's rarest types of fish and other water-life.

The mission's twin submersibles, used last year to plant a Russian flag on the North Pole seabed, slipped into the choppy waters just after dawn and descended 1,680 meters to the lake's deepest point, setting a world record for freshwater submersion.

Each of the bright-red Mir-1 and Mir-2 craft carried three scientists. Chilingarov was with reporters who watched from a mission-control point on a nearby platform.

Russian officials hailed the five-hour expedition, due to take seabed samples and document Baikal's unique flora and fauna, as a new chapter in Russian science. "This is a world record," Interfax news agency quoted one of the expedition's organisers as saying.

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