Russia has blocked the entry of a Greenpeace boat into its waters, the environmental activist group said Wednesday, suggesting that its attempts to stage a peaceful protest were blocked in order to hide the extent of a oil exploration program in operation by Exxon Mobil and Russia's energy giant Rosneft.

Greenpeace said its icebreaker Arctic Sunrise was repeatedly denied entry into the portion of the Kara Sea where the joint oil exploration endeavor is underway offshore north of western Siberia. Russian authorities reportedly said that the Arctic Sunrise was not equipped to handle the thick sheets of ice that cover much of the water's surface in the Northern Sea Route.

But Greenpeace contends its vessel is just as seaworthy as the 400 other ships which have been allowed entry into the Arctic waters.

"This is a thinly veiled attempt to stifle peaceful protest and keep international attention away from Arctic oil exploration in Russia," Greenpeace campaigner Christy Ferguson said, according to the Guardian"The Arctic Sunrise is a fully equipped icebreaker with significant experience of operating in these conditions, while the oil companies operating here are taking unprecedented risks in an area teeming with polar bears, whales, and other Arctic wildlife."

Greenpeace protests the exploration and future drilling of oil in the Arctic, citing potential spills and damage to an environment already under the stress of climate change.

"The Arctic is under pressure from oil companies seeking to exploit its fossil resources. They see the melting of the sea ice not as a warning but as a business opportunity," the Greenpeace campaign Into the Arctic states on its webpage.

According to Greenpeace, state-owned Rosneft is the world's largest oil company. "It holds over a million square kilometers of license blocks on the Arctic shelf, and plans to drill the first exploratory well as soon as 2014 at Vostochno-Prinovozemelsky-1 block located next to the Russian Arctic National Park," Greenpeace wrote on its Into the Arctic blog.

According to a 2012 Exxon Mobil corporate report, the company has "multiple areas of exploration interest in the Russian Arctic."

In 2011 Exxon Mobil and Rosneft signed an agreement to jointly explore for hydrocarbon resources in the Kara Sea, which Exxon says is "among the world's most promising and least explored offshore areas with a high potential for oil and natural gas."

Exxon Mobil has a stake in the Kara Sea equivalent in size to its total leased acreage in the entire U.S. Gulf of Mexico.

The drilling of the first exploration well is expected as between 2014 and 2015, the report stated, adding that work is underway to initiate pilot development drilling in late 2013.