Oil giant Shell has been given final permission for an exploratory drilling project in Alaskan waters, a setback for environmental groups that have strongly opposed the controversial project.

The drilling, already underway with a temporary permit, is the first of its kind since Shell's 2012 Arctic drilling project was plagued by problems.

The Bureau of Safety and Environmental Enforcement announced the permit Monday.

"Activities conducted offshore Alaska are being held to the highest safety, environmental protection, and emergency response standards," said director of the bureau Brian Salerno in a statement.

US President Barack Obama angered environmentalists by authorizing Arctic drilling projects in May.

Environmental groups including Greenpeace have strongly protested the drilling, even blocking the exit of Arctic-bound offshore rigs from west coast ports.

At the end of July, Shell resumed its exploratory drilling after one of its icebreakers was delayed for nearly two days by protesters.