Russia's oil producer Rosneft asked Lukoil to cancel a crude oil purchasing contract with Bashneft, which RBC daily put at 400 billion rubles ($6.4 billion).
Earlier this month Rosneft acquired just over 50% in Bashneft for 330 billion rubles as part of a government privatization.
Rosneft asked Lukoil to annul the agreement with Bashneft, according to which Lukoil supplied Bashneft's refineries with crude oil and received oil products, Reuters reports.
"The proposal was supported by Lukoil," a Rosneft's spokesman said without valuing the deal.
Rosneft appointed its own representative to govern Bashneft almost immediately after acquiring control.
Basheft's total refining capacity stands at 23.2 million tonnes per year.
