Activists from environmental lobby group Greenpeace on Tuesday challenged a ship from Russian oil giant Rosneft in the Barents Sea, in a bid to stop oil exploration work they say is harming the Arctic ecosystem.

Rosneft, which has been increasingly targeted by campaigners over its Arctic shelf exploration drive, dismissed Greenpeace's concerns and said the seismic survey was being strictly monitored for its environmental impact.

Greenpeace said in a statement that its ice breaker ship Arctic Sunrise had confronted the Rosneft-contracted vessel Akademik Lazarev which was firing deep underwater sound cannons for seismic testing.

A Greenpeace activist on the Arctic Sunrise told AFP by satellite phone that campaigners had launched smaller speedboats that came within 100 metres of the Russian vessel.

"We we are bearing witness, showing our presence and exposing what is happening. These oil companies think they can operate in remote regions without scrutiny," Greenpeace Arctic campaigner Christy Ferguson said from the Arctic Sunrise.

"We went out in the zodiacs (lifeboats) to get close to the vessel. Next to the ship, we could hear the sounds from the seismic vessel's blasts."

"It was so loud you could hear it and even feel it, although it was underwater. We plan to continue over the next (few) days to have a presence around the ship."

The seismic testing is used to draw up undersea maps ahead of drilling and Greenpeace said the decibel levels employed risk causing deafness or even death to marine mammals.

Ferguson said the Greenpeace campaigners contacted the Akademik Lazarev's captain by radio, demanding that the vessel cease its operations and warning him the results would be used to advance a potentially devastating oil project.

"We demanded they cease their activities as they are preparations for dangerous drilling and return to port," she said.

"After that I had a conversation with the captain until he cut off contact... about the impact of their activities on whales and other wildlife."

Greenpeace says the Barents Sea is home to narwhals, bowhead whales, walruses and polar bears, and Ferguson said the campaigners were particularly concerned to see a pod of dolphins close to the testing site.

Exploiting Russia's vast Arctic energy reserves has become a major strategic priority for Rosneft, which has signed exploration cooperation deals with BP, ExxonMobil and Statoil.

Rosneft insisted it carefully follows environmental regulations and said it was using sophisticated modern technologies that follow international regulations.

"Rosneft executes its exploration programme in the Barents Sea in compliance with all environmental requirements of the Russian law and the license agreements," it said in a statement to AFP.

"During the seismic survey, a programme of environmental monitoring and safe operations control are being implemented."

However Greenpeace accuses Western oil giants of wanting to work in Russia to take advantage of environmental protection practices that are more relaxed than in their home countries.

It said companies are now exploiting melting sea ice to move into new territories for exploration. "Drilling for oil in the harsh and unpredictable Arctic environment is extremely risky," said Greenpeace.