A Greenpeace icebreaker protesting oil prospecting in the Arctic said it would leave after Russia threatened to use force against the Dutch-flagged vessel including firing on it, the group said Monday.

The Arctic Sunrise entered the Northern Sea Route without permission on Saturday to call attention to plans by Russian top oil firm Rosneft and its US partner ExxonMobil to drill in a remote natural reserve.

The ship approached the site of the planned protest in the Kara Sea unhindered but on Sunday the Russian coast guard inspected the vessel "without permission" and asked the ship to leave the area, the group said.

"The coast guard warned the ship it would use force if necessary, including opening fire on the ship, if the Arctic Sunrise would not leave," Greenpeace said in a statement.

The environmental group said it would leave to avoid any risk to the crew but would call on the Dutch government "to consider a legal complaint against Russia's violation of international law of the sea and freedom of expression."

"We are a peaceful protest ship and have done nothing to warrant the threat of force against us," Christy Ferguson, a Greenpeace Arctic campaigner aboard the ship, was quoted as saying in the statement.

"We won't be intimidated into silence."

The Russians boarded the icebreaker after the group dispatched inflatable boats with banners reading "Save the Arctic" near the Geolog Dmitry Nalivkin, an oil exploration vessel contracted by Rosneft and ExxonMobil, it said.

On Sunday, "the Russian coast guard announced the creation of a four nautical mile 'exclusion zone' around the Geolog Dmitry Nalivkin, preventing the activists from obtaining clear images of the vessel," Greenpeace said.

Last week Greenpeace said Russia had refused permission to enter the Northern Sea Route on several occasions citing concerns about the icebreaker's ability to withstand thick ice.

The global environmental group has called the move "a thinly veiled attempt to stifle peaceful protest".

The Russian transportation ministry has accused the Greenpeace vessel of "crudely" violating Russian and international law.

The transportation ministry said Saturday that it had sent a letter to the foreign ministry with a request to get in touch with The Netherlands' maritime authorities "with the aim of influencing the owner of the vessel on behalf of the flag state".

The Russian foreign ministry has not publicly reacted so far.

The Netherlands said Sunday that Greenpeace's right to peaceful protest was "indisputable," adding that there was no reason to doubt the ship's technical state.

Greenpeace said the plans to drill in the Russian Arctic National Park were in contravention of Russia's own laws.

Established in 2009, the nature reserve is home to endangered species such as the bowhead whale, and it is a major breeding ground for polar bears.

Rosneft, headed by one of President Vladimir Putin's closest confidants, Igor Sechin, has said its offshore operations were "absolutely safe".

Russia and the United States hope that the global warming melting the Arctic sea ice will help them tap the vast oil and gas resources believed to be buried in the region.

Russia has pledged to turn the Northern Sea Route into a key shipping artery, part of the Kremlin's bid to mark out its stake over the energy-rich Arctic.

Putin, who has made much of his concern for wildlife, has in the past been pictured kissing wild animals and sea mammals.