And they contain more ice than was previously estimated, meaning they could raise sea level by more than predicted, the international team of researchers writes in the journal Science.

"The ... Amundsen Sea glaciers contain enough ice to raise sea level by 1.3 meters (4 feet)," the researchers wrote in their report.

"Our measurements show them collectively to be 60 percent out of balance, sufficient to raise sea level by 0.24 mm (nearly 0.01 inch) per year," they added.

And as the surrounding ice shelves melt - which they are doing - this process will speed up, the researchers said.

"The ice shelves act like a cork and slow down the flow of the glacier," said Bob Thomas of the NASA Goddard Space Flight Center's Wallops Flight Facility in Virginia.

Theirs is the second report this week to warn of rapidly melting glaciers in Antarctica.

On Tuesday a team at NASA and the University of Colorado reported that the 2002 breakup of the Larsen B ice shelf on the other side of the continent had accelerated the breakup of glaciers into the Weddell Sea.

Many teams of researchers are keeping a close eye on parts of Antarctica that are steadily melting.

ICE SHELVES

Large ice shelves in the Antarctic Peninsula disintegrated in 1995 and 2002 as a result of climate warming. But these floating ice shelves did not affect sea level as they melted.

Glaciers, however, are another story. They rest on land and when they slide off into the water they instantly affect sea level.

"The rates of glacier change remain relatively small at present," said Eric Rignot of NASA's Jet Propulsion Laboratory in Pasadena, California, who worked on Friday's study.

"But the potential exists for these glaciers to increase global sea level by more than one meter (3 feet). The time scale over which this will take place depends on how much faster the glaciers can flow, which we do not know at present."

The measurements also show the glaciers are thicker than once believed. This means more melting and more rapid melting, Thomas said.

"Our measurements show an increase in glacier thinning rates that affects not only the mouth of the glacier, but also 60 miles to 190 miles inland," Thomas said in a statement.

The researchers from NASA, the Centro de Estudios Cientificos in Chile, the University of Kansas and Ohio State University wrote their estimates based on satellite data and measurements from a Chilean P-3 aircraft equipped with NASA sensors.

Experts say that overall sea levels around the world are going up by about 1.8 mm or 0.07 inch a year. About half of this comes from melting ice in glaciers.

The melting into the Amundsen sea is now more than the previous amount from all of Antarctica and more than the estimated contribution from Greenland, the researchers said.