MOSCOW - A Siberian oilfield that Russia and China plan to develop together was the site of Soviet nuclear blasts in the 1970s and 1980s, Russian officials said on Friday.
The government and state oil firm Rosneft said the field was safe, rejecting environmentalists' concerns that oil extracted from it could be contaminated with radiation.
But the revelation raises questions for a strategic joint venture announced a week ago in which Russia, the world's top energy producer, ceded a share of its oil wealth to China, the leading consumer.
At least seven "peaceful" nuclear detonations were performed at the Srednebotuobinskoye oilfield, according to a report published by the environment ministry of the Republic of Sakha, a remote region in Eastern Siberia also known as Yakutia.
"Yes, indeed, there were nuclear explosions performed at the site," a ministry spokeswoman told Reuters from the city of Yakutsk. No radiation leaks were reported, she said.
Blasts at the field were intended to increase flows from oil-bearing rock and, in one case, create a storage reservoir.
Rosneft said in comments emailed to Reuters that it regularly monitors radiation at the blast sites - now mothballed - in areas where it holds production licenses.
"Radiological examination of the deposits and the production extracted from them shows that no radionuclides have reached the surface - including in the oil," it added.
The company last week signed a joint venture memorandum with China National Petroleum Corp (CNPC) to develop the 1-billion-barrel oilfield. CEO Igor Sechin signed an agreement this week that would raise Rosneft's exports to China to more than 1 million barrels per day.
The deals reflect President Vladimir Putin's drive to pivot Russia's energy export strategy eastward, away from Europe's stagnating market and to the more dynamic Asia-Pacific region.
Rosneft did not say whether it had told CNPC about the blasts. CNPC could not provide immediate comment on the issue.