"Their ship is currently at 86 degrees of latitude. The descent will be on August 1," a spokeswoman for the Arctic and Antarctic Institute in Saint Petersburg told AFP on Tuesday. The North Pole is at 90 degrees.

The Arctic 2007 expedition led by parliament member Artur Chilingarov aims to advance Russian claims to a swathe of Arctic seabed thought to be rich in oil and gas amid heightened international rivalry in the region.

The mini-subs are to descend about 4,200 metres (14,000 feet) to the seabed at the North Pole where they will carry out tests and leave a Russian flag in what Russian officials describe as the first-ever such dive.

The Russian expedition hopes to establish that a section of sub-sea territory known as the Lomonosov Ridge, which includes the North Pole, is in fact an extension of Russia.

After the descent to the polar seabed the researchers will go on to establish a "drifting ice station" on a suitable piece of ice, which will be home to 11 scientists studying climate issues.