WASHINGTON—As declining sea ice and better mapping and technology make the Arctic more accessible, nations with interests there, including the United States, are beginning to stake their claims on the resource-rich region.

Russia planted a flag on the seafloor below the North Pole in 2007. Denmark announced this week that it would ask the United Nations to recognize the North Pole as an extension of Greenland, its territory. The US sent the secretary of state to a meeting of eight Arctic nations earlier this month for the first time, a sign that Americans also have their eye on the region’s potential resources.

“This region matters greatly to us,” Secretary of State Hillary Clinton said after the conference in Nuuk, Greenland. The US is committed to the Arctic Council’s mission, as well as the challenges the Arctic faces, Clinton said, including possible resource development.

Although numerous logistical challenges to oil and gas exploration in the region remain, the US Geological Survey estimates that as much as a third of the world’s undiscovered gas and 13 percent of its undiscovered oil may be in the offshore Arctic, in relatively shallow water.

“The melting of sea ice, for example, will result in more shipping, fishing and tourism, and the possibility to develop newly accessible oil and gas reserves,” Clinton said. “We seek to pursue these opportunities in a smart, sustainable way that preserves the Arctic environment and ecosystem.”

The US has been slow to recognize not just the importance of the Arctic but also the implications of the melting ice and what it means for commercial and economic interests, said John Bellinger III, who was a senior adviser to Condoleezza Rice when she was the secretary of state in the George W. Bush administration. Other nations have been far more focused on the region, while the US has been distracted by other events.