The conditional approval follows comprehensive review of comments from the public, Alaska Native organizations and state and federal agencies, BOEM said.

However, the multi-year drilling program is subject to other permits from state and federal agencies, including one to drill from the Bureau of Safety and Environmental Enforcement and authorizations under the Marine Mammal Protection Act.

BOEM director Abigail Ross Hopper said: "We have taken a thoughtful approach to carefully considering potential exploration in the Chukchi Sea, recognizing the significant environmental, social and ecological resources in the region and establishing high standards for the protection of this critical ecosystem, our Arctic communities, and the subsistence needs and cultural traditions of Alaska Natives.

"As we move forward, any offshore exploratory activities will continue to be subject to rigorous safety standards."

Under the revised exploration plan, Shell plans to drill up to six wells within the Burger Prospect using the drillship Noble Discoverer and the semi-submersible drilling unit Transocean Polar Pioneer.

The oil drilling program in Chukchi Sea will resume this year, following a nearly two-year suspension.

Shell suspended drilling in 2013 after the grounding of a drilling rig.

However, the move is being opposed by environmentalists.

World Wide Fund managing director of US Arctic programs Margaret Williams said: "Today’s decision to move closer to allowing fossil fuel extraction from the Chukchi Sea — home to majestic wildlife and a place where extreme weather, gale-force winds, and rough seas make operations and response to spills extremely difficult — is a backward move at this time.

"Without proven technologies to clean up potential spills, offshore drilling is too great a risk to America’s Arctic. We have so many better energy choices, including promising technologies that provide clean ways to power our lives without harming the planet."

The Arctic is estimated to have approximately 20% of the world’s unclaimed oil and gas reserves.