INUVIK, Northwest Territories — Beneath the melting ice of the Arctic Ocean, the world’s last great land grab is under way.

Global warming is opening the Northwest Passage that sailing ships sought 500 years ago, and some of the world’s biggest oil reserves are becoming accessible under the polar sea. Russia, America, Canada, Norway, and Denmark are jockeying for territory in moves that could end up in clashing claims.

With an eye on asserting Canada’s stake, Canada’s prime minister, Stephen Harper, and his cabinet will travel this week to the Arctic town of Inuvik, as the country completes its largest-ever military exercise in the region. The town, where the summer sun never sets, lies 2,548 miles from Ottawa.

“You have the recipe for trouble if there isn’t real energy invested early to help resolve some of these issues,” a fellow at the Council on Foreign Relations in New York, Scott Borgerson, said. “You can envisage a future in which all the ice is gone, there is this wild-west environment in terms of lack of respect for whatever national law.”

Western nations are playing catch-up in laying claim to the Arctic. Russia, which planted a titanium flag on the Arctic seabed last year, already deploys strategic-bomber flights to patrol the region. It has also begun training troops for combat in the far north, where temperatures can drop to less than -70 degrees Fahrenheit.

If Arctic disputes come to a head, the divide between leaders in Moscow and the West may soon stretch beyond Georgia, where a war with Russia broke out this month over the breakaway region of South Ossetia.

“Events in Georgia should wake people up to what the Russians have been doing,” an associate director of the University of Calgary’s Center for Military and Strategic Studies, ” Rob Huebert, said.