The United States and Canada will freeze future oil and gas drilling in their Arctic waters, a move applauded by environmentalists but denounced by the energy industry.
The White House said on Tuesday that US President Barack Obama is making the most of the Chukchi Sea and Beaufort Sea, bordering Alaska, off limits to offshore oil and gas leasing.
Canada, meanwhile, will make all Canadian Arctic waters no-go zones for energy drilling, but will review the decision every five years.
"These actions, and Canada's parallel actions, protect a sensitive and unique ecosystem that is unlike any other region on Earth," Obama said in a statement.
He noted that, even with high safety standards, the risks of an oil spill in the fragile and remote environment were too high.
Obama made the move under a provision of a 1953 law that allows the president to remove areas from offshore drilling, and there is no provision for future presidents to roll it back, US officials said.
'Unique and vibrant ecosystems'
The move aims to protect the "incredibly unique and vibrant ecosystems", the interests of indigenous people, and to minimise oil spill risks.
Obama will also ban new oil and gas leases along the US Atlantic coast from New England to Virginia.
Sally Jewell, interior secretary, said the move would help support fishing and protect the marine resources of Alaska native communities.
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She said it recognised the vulnerable marine environments in the Arctic and Atlantic oceans, their irreplaceable ecological value, and "the unique role that commercial fishing and subsistence use plays in the regions' economies and cultures".
Greenpeace praised Obama and said he should do more to stop any new fossil fuel infrastructure that would lock in the worst effects of climate change.
"We know now, more clearly than ever, that a Trump presidency will mean more fossil fuel corruption and less governmental protection for people and the planet, so decisions like these are crucial," spokesman Travis Nichols said.
David Miller, president and chief executive of World Wildlife Fund - Canada, called the actions "significant steps toward the protection of the Arctic's unique ecosystems".
He named ice-dependent wildlife - including polar bears, narwhal, seals, walrus, and beluga and bowhead whales - as some of the animals that will benefit.
The moves do not affect existing leases, and exclude one area near shore in the Beaufort Sea that is adjacent to existing leases, a senior US official said.
The decision should have minimal impact on US industry because little drilling is going on in the region and development is expensive and would take years, the official said.
But the American Petroleum Institute, an industry group, said the move was short-sighted and endangered national security.
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"Our national security depends on our ability to produce oil and natural gas here in the United States," API director Erik Milito said.
He claimed there is "no such thing as a permanent ban" and said the industry would work with the new administration to reverse it.
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The move seems designed to tie the hands of Obama's right-wing successor Donald Trump, who has named several officials close to the oil industry to his cabinet.
Trump picked a renowned climate change denier and fossil fuel industry defender last week as his top environmental official.
Source: Al Jazeera and news agencies