Moscow and Minsk have been trying to hammer out a deal on annual Russian oil sales to Belarus, an issue that has disrupted oil flows to Europe in the past.
In January, when negotiations hit a dead end, Russia halted oil sales to Belarus, though onward supplies to Europe were not interrupted. The issue was eventually resolved after lengthy talks.
The sources told Reuters that Belarus state energy company Belneftekhim had notified Russian pipeline operator Transneft that it wanted to increase the transit tariff via the Druzhba pipeline for Russian suppliers by almost 25% from Jan. 1, 2021, much higher than envisaged by Moscow.
It is expected that Belarus and Russian government officials will join Russian oil company managers in a meeting on Thursday to discuss oil supply terms for the next year, two of the sources said.
The Russian Foreign Ministry has said that Moscow's top diplomat, Sergei Lavrov, plans to hold a working visit to Belarus on Wednesday and Thursday, when a meeting with Belarusian leader Alexander Lukashenko could also be on the agenda.
The talks have been taking place amid street protests in Minsk after the Aug. 9 presidential election, at which Lukashenko claimed the victory. The opposition has said the vote was rigged, an accusation denied by the authorities.
Moscow has supported Lukashenko, with Russian President Vladimir Putin agreeing a $1.5 billion loan to provide much-needed support in a crisis worsened by the pandemic.
The oil talks have also been bogged down by other unresolved issues between the countries, including natural gas sales as well as compensation for Russian-contaminated oil supplies.
Belneftekhim, Transneft and the Russian energy ministry did not respond to requests for comment.
(Reporting by Gleb Gorodyankin, Olesya Astakhova and Olga Yagova; Additional reporting by Vladimir Soldatkin; Editing by David Goodman)