A deal between Russia and Norway on Arctic boundaries offers a "hopeful sign" that Moscow is taking a cooperative approach to disputes in the oil-rich region, a US defense official said on Wednesday.

The accord unveiled in Oslo on Tuesday, which ended a 40-year dispute over maritime borders, marked a "historic" breakthrough, said Alexander "Sandy" Vershbow, assistant secretary of defense for international security affairs.

"I think yesterday's Norwegian-Russian agreement is another hopeful sign that Russia's policy in the Arctic is going to be grounded on cooperation and a search for common interests," Vershbow told a conference on the Arctic.

"Certainly we need to encourage that approach."

Vershbow, a former ambassador to Moscow, said Russia needed to be judged on its actions and not necessarily some strident comments by parliament members.

"While some Russian politicians have engaged in flamboyant rhetoric about Russia's claims in the Arctic, the Russian government has taken a constructive approach," including leading an international task force with the United States on search and rescue efforts, he said.

Melting polar ice and new technologies have made the "high north" more accessible and fueled competition for oil and gas reserves in the Arctic.

Canada, Denmark, Norway, Russia and the United States are at odds over how to divvy up the Arctic seabed, thought to hold about 90 billion barrels of oil and 30 percent of the world's undiscovered gas resources, according to the US Geological Survey.

Three countries, Canada, Russia, and Denmark, claim the North Pole as their own and in 2007, a Russian mini-submarine reached the bottom of the Arctic Ocean under the North Pole and planted a Russian flag.

Vershbow said climate change in the Arctic presented a pivotal choice for countries with interests in the region, saying Washington would work to promote cooperative approaches.

"We have plenty of time to get it right," he said.

Norway's deputy defense minister, Espen Barth Eide, said at the same conference that the agreement with Russia came about partly because existing international maritime law, in the form of the UN Convention on the Law of the Sea, offered a framework to reach a compromise.

The US Senate has yet to ratify the convention.

Eide said Norway hoped the deal with Russia could serve as an "inspiration" for other countries facing similar disputes, and warned against overly dire predictions of looming tensions in the Arctic.

Global warming in the Arctic represents "change of potentially large geopolitical dimensions," he said.

But "it's not an open void in a completely uncontrolled circumstance which will end up in some kind of resource war," he said.

The issue has "been placed on the agenda where it should be as a crucial theme...but it's not an issue which necessarily should lead to a dramatic and violent conflict."

He also said it was "logical" that countries would deploy some military forces in the Arctic, not to gird for war but because increased commercial and other activity would require armed forces that were best equipped to carry out rescue efforts and monitoring in difficult conditions.

"But it's important that it is calibrated in such a way so we are not militarizing issues that are better solved in the civilian field," he said.