US activists are reigniting efforts to stop Arctic oil drilling, after the Obama administration gave a conditional approval to Royal Dutch Shell's exploration plan. 

The move is seen as a major win for the oil industry, which has long wanted to drill in the Chukchi Sea off the coast of Alaska. An estimated 20 per cent of the world's undiscovered supply of oil and natural gas is located in the Arctic. Environmentalists warn that drilling in the icy water could lead to a major ecological disaster.

On Tuesday, a group of activists in the US city of Seattle set up a large tripod to block the entrance of a fuel station. Drill ships are expected to arrive in the area later this week.