Environmental campaigners today claimed to have shut down a "dangerous" oil drilling operation by a British energy company in the Arctic.
Greenpeace said four expert climbers in inflatable speedboats had evaded Danish navy commanders to climb up the inside of the Cairn Energy oil rig off Greenland.
The four campaigners are now hanging from the rig 15m above the icy Arctic ocean in tents suspended from ropes, halting its drilling operation, Greenpeace said.
The campaigners, who are protesting against what they claim are the "huge risks" energy companies are taking with the environment by drilling for oil in deep water, say they have enough supplies to occupy the tents for several days.
They claim that if they halt drilling for a short time, Cairn will struggle to meet the deadline to complete exploration before the winter conditions set in, forcing the company to abandon the search for oil off Greenland until next year.
Sim McKenna, from the US, who is one of the climbers, said: "We've got to keep the energy companies out of the Arctic and kick our addiction to oil, that's why we're going to stop this rig from drilling for as long as we can.
"The BP Gulf oil disaster showed us it's time to go beyond oil.
"The drilling rig we're hanging off could spark an Arctic oil rush, one that would pose a huge threat to the climate and put this fragile environment at risk."
The Greenpeace ship, the Esperanza, set sail from London last month with a pledge to target what the environmental group described as one of the 10 most dangerous deep water drilling sites in the world.
Greenpeace said it wanted to highlight problems with oil that went "far beyond" the disaster at BP's Deepwater Horizon rig in the Gulf of Mexico, and pledged to confront the industry head-on over its "reckless" pursuit of oil.
Last week the campaigners said they were confronted by a Danish warship sent to protect the drilling operation in the seas off Greenland, as the Esperanza approached the site.
Greenpeace said it had been warned that the ship would be raided and the captain arrested if it breached a security zone set up in the area.
The following day, Cairn announced it had found gas in thin sands at the site - an indication there could be oil in the area.
The campaigners are concerned that a discovery of oil could prompt an oil rush by major companies in the Arctic, threatening the fragile environment of the region and providing a new source of a fossil fuel which contributes to climate change.
Greenpeace campaigner Leila Deen, from London, speaking from the Esperanza, said the climbers wanted to stop the drilling - which should have halted when the activists breached a 500m (547-yard) cordon around the rig - for as long as possible.
"Cairn have quite a short window in which they can drill up here because the seasons change and the ice comes in."
The environmental group had targeted the Cairn exploration rig in the Arctic because the region "is really symbolic of the state of crisis the world is in", she said.
"We're facing catastrophic climate change, yet the oil companies drill for the last drop of oil.
"It brings it all home to see tugs pulling icebergs away from the rig - it shows how far we've gone to keep our addiction to fossil fuels going."
She said the exploration of the virtually untouched region, where seals, humpback whales and sea lions could be seen, showed what was wrong with the oil industry and the world's addiction to oil.
She also said it highlighted the impact of fossil fuels on climate change, with Greenland glaciers melting and icebergs falling into the sea as a result of warming temperatures.
At the height of the BP oil spill crisis in the Gulf of Mexico, marine pollution experts warned the "nightmare" oil spill would be one that stemmed from drilling in the Arctic.
They warned that, in an Arctic spill, oil would only evaporate and break down slowly and would affect the "albedo", or reflective, effect of the region which helps maintain its climate.