Two deep-diving Russian miniature submarines on Thursday descended more than 2Ѕ miles (4 kilometers) to the ocean floor beneath the North Pole, the ITAR-Tass news agency reported.
Expedition leader Artur Chilingarov, who was aboard the MIR 1 three-person sub, told colleagues on a research ship on the surface that his craft had reached the seabed. "The landing was smooth, the yellowish ground is around us, no sea dwellers are seen," he said, according to Tass.
In a perilous project mixing science, exploration and the scramble for potential oil and gas fields, crews of the MIR 1 and MIR 2 are engaged in what Russian authorities called the first dive to the ocean floor at Earth's northernmost point.
The crew of the MIR 1 planned to drop a titanium capsule containing the nation's flag on the bottom, symbolically claiming almost half of the planet's northern polar region for Moscow.
Chilingarov, 68, a famed polar scientist, spoke of the danger of the expedition in comments broadcast on Russia's NTV television before he boarded the first sub. "I am scared and I don't hide it," he said.
Expedition members say the biggest challenge for the sub crews will be to find their way back to an opening in the surface of the 1.5 meter (5 foot) thick polar pack ice after their dive. They must resurface before exhausting their air supplies.
Researchers mapped the location of the natural openings in the ice before the dives. The atomic-powered icebreaker Rossiya spent most of Wednesday night and Thursday morning carving a 125-by-10 meter (410 foot by 33 foot) artificial opening near the pole, RTR television reported.
U.S. State Department spokeswoman Leslie Phillips said, "We wish the Russian scientists a safe expedition."