Mike Pompeo, the US secretary of state, has rejected Canada's claims to the Northwest Passage as "illegitimate", in a high-profile foreign policy speech that prompted frustration and surprise among experts and government officials.

Delegates from Arctic nations – Canada, Denmark, Finland, Iceland, Norway, Russia, Sweden and the US – had gathered in Finland to discuss balancing climate change with resource development in the region.

"No one denies Russia has significant Arctic interests," Pompeo told delegates of the Arctic Council on Monday. "We recognize that Russia is not the only nation making illegitimate claims: the US has a long contested feud with Canada over sovereign claims through the Northwest Passage."

The Arctic route linking the Atlantic and the Pacific offers a potential shortcut between Europe and China. Although the passage remains ice-bound for much of the year, it has become increasingly usable because of global warming and the retreat of Arctic sea ice.