The United States has called for increased protection of polar regions, including tighter restrictions on Antarctic tourism and increased funding for environmental research there and in the Arctic.

U.S. Secretary of State Hillary Clinton outlined Washington's proposals to help protect polar regions Monday at the opening of a two-week conference of signatories to the 50-year-old Antarctic Treaty.

Clinton said the recent collapse of an Antarctic ice bridge was a stark reminder that the poles are gravely threatened by climate change and human activity.

"With the collapse of an ice bridge that holds in place the Wilkins Ice Shelf, we are reminded that global warming has already had enormous effects on our planet and we have no time to lose in tackling this crisis," she told the first-ever joint meeting of Antarctic Treaty parties and the Arctic Council at the State Department in Baltimore.

The bridge linking the Wilkins shelf to Antarctica's Charcot and Latady Islands snapped on Saturday after two large chunks of it fell away last year. The shelf had been stable for most of the last century before it began retreating in the 1990s.

She said the administration of U.S. President Barack Obama will propose mandatory limits on the size of Antarctic cruise ships and the number of passengers they bring onshore.

Could be model for Arctic

Clinton said the Antarctic Treaty — which prevents military use on the continent and promotes international scientific research — could be a model for improved co-operation and co-ordination in the Arctic, which is not governed by a similar pact.

"The treaty is a blueprint for the kind of international co-operation that will be needed more and more to address the challenges of the 21st century," she said.

Clinton predicted "catastrophic consequences" unless quick action is taken.

"The changes underway in the Arctic will have long-term impacts on our economic future, our energy future, and indeed, again, the future of our planet, so it is crucial that we work together."

Several northern countries, including Canada and the U.S., are hoping to assert their sovereignty on northern coastal areas beyond the 200 nautical-mile economic zones they already claim.

In order to claim areas of the seabed — which could be rich in resources such as oil and gas — each nation must gather extensive scientific mapping data on the sea floor.

Washington also disputes Canada's claim of sovereignty over the Northwest Passage, an Arctic sea route that stretches between the Atlantic and Pacific Oceans.

With files from the Associated Press