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* Coastguard fires shots over Greenpeace vessel-group
* Similar protest action last year delayed operations
* Greenpeace says Russia cannot guarantee safety of rig
MOSCOW, Sept 18 (Reuters) - Greenpeace said on Wednesday twoof its activists scaled the Prirazlomnaya oil platform in Arcticwaters in a fresh protest over the potential threat to theenvironment from operations slated to start by the end of theyear.
Production at the Gazprom-owned rig, Russia'sfirst such project in the Barents Sea, was delayed last yearafter similar action. Gazprom put the delay down to "technicalreasons".
Hydrocarbon production in its vast offshore areas is seen byRussia as vital to maintaining oil output, the world's largest,at no less than 10 million barrels per day this decade.
Global majors including ExxonMobil, Eni andStatoil have agreed deals with Russia's top oilproducer Rosneft to enter the region. Their projectsare not expected to begin extracting oil before the 2020s.
Greenpeace said in an emailed statement it sent five boatsto the rig early on Wednesday. One was arrested by the Russiancoastguard which fired warning shots across the bows of itsArtic Sunrise base vessel.
It said two of its members climbed the rig and would remainthere as long as possible.
"Despite massive financing for Prirazlomnaya, it is not ableto guarantee safe production of Arctic oil," Greenpeace said.
Offshore safety concerns have grown after BP's Deepwater Horizon oil rig exploded in 2010, killing 11 workersand spewing millions barrels of oil into the Mexican Gulf.
Prirazlomnoye is the first Arctic offshore oil deposit to bedeveloped by Russia and is located in the Pechora Sea, a part ofthe Barents Sea, 60 km (40 miles) from the northern coast.
It is expected to reach peak production of 6 million tonnesper year (120,000 barrels per day) in 2019.
Gazprom Neft, the oil arm of state gas exportmonopoly Gazprom, is expected to obtain a licence to develop thefield. It expects overall investment in the project to be around200 billion roubles ($6 billion), of which half had already beenspent.
Gazprom Neft and Gazprom declined immediate comments.
