The huge lake more than 2 miles under the ice sheet was reached after years of drilling, a news agency said.
Russian scientists have drilled into the vast, dark and never-before-touched Lake Vostok 2.2 miles below the surface of Antarctica, the state-run Russian news agency RIA Novosti said Monday.
"Yesterday, our scientists stopped drilling at the depth of 3,768 meters and reached the surface of the subglacial lake," the news agency quoted a source as saying. The team "finally managed to pierce" the ice sheet into Vostok, the source said.
The report could not be verified Monday, but numerous Antarctica experts in the United States said they were hearing the same unconfirmed news. Sergei Lesenkov, spokesman for the Arctic and Antarctic Scientific Research Institute, told Agence France-Presse in Moscow on Monday that there was the possibility of a "fundamental scientific development."
It has taken the Russians more than 20 years to drill into the lake, operating in some of the most brutal weather conditions in the world. Their reported accomplishment comes just as the Antarctic summer ends at Vostok and the cold becomes so great that machinery can't be operated and airplanes can't come in or go out.
Because reaching the lake has been a high Russian priority in terms of the science and the engineering prowess it would suggest, a formal announcement is anticipated.
The Russian effort has created scientific excitement about potentially learning some of the long-held secrets of the largest subglacial lake in Antarctica, a body of water that wasn't discovered until the mid-1990s and is the world's third-largest lake by volume.
The long effort has met with controversy over some of the chemicals and techniques used in the drilling. Many have been concerned that pristine Lake Vostok -- which hasn't felt the wind for more than 20 million years and may well be home to previously unknown life forms -- could be contaminated by the kerosene, Freon and other materials used in the drilling.
John Priscu of Montana State University, an Antarctica specialist who has been in periodic contact with the Russian team, said that rumors were flying that the lake was indeed pierced but that no information has been formally announced.
"If they were successful, their efforts will transform the way we do science in Antarctica and provide us with an entirely new view of what exists under the vast Antarctic ice sheet," he said in an e-mail.
Many scientists see Vostok as not only a last frontier on Earth, but also a potential gold mine for learning about possible conditions on Jupiter's moon Europa or Saturn's moon Encedadus. Each is covered by a thick shell of ice with liquid water below, warmed by either the inner heat of the moon or by tidal forces.
The Russians' plan for this year's Lake Vostok expedition has been to use a thermal drill on the last 30 feet of ice, pierce the lake and draw some of the water a short way up the borehole. The water will then freeze and be extracted later.