Rosneft, which last year bought mid-sized oil producer Bashneft, produced 210 million tonnes (4.2 million barrels per day) of oil in 2016, accounting for 40 percent of Russia's total output. It said the Kondaneft fields' reserves stand at 157 million tonnes.

"The company will take measures to quickly commission Kondaneft oilfields in 2017, which will allow for a significant growth in Rosneft's consolidated output," it said in a statement.

Local press said the asset asset had been bought from NNK, a company headed by former Rosneft chief Eduard Khudainatov. Rosneft declined to comment on the identity of the seller, though the fields are listed as NNK-owned on the NNK website.