Russia has halted oil supplies to Belarus amid a disagreement over tariffs, according to officials at a Belarusian oil refinery in the northern city of Navapolatsak.
The officials told RFE/RL that the shipments stopped on January 1 and the facility is currently processing only Russian oil delivered before that date.
Belarus has been at odds with Russia over oil-transit prices for some time against a backdrop of increasing pressure by Moscow on Belarusian President Alyaksandr Lukashenka to deepen integration between the two countries.
A two-month deal on natural-gas prices hours before a December 31 deadline helped the sides avoid a gas shutoff to start the year.
Belarus is heavily reliant on Russia for fuel and funding and is a key transit route for Russian energy supplies to Europe. And now, Russia has just broken a new oil production record.
Moscow and Minsk signed an agreement in 1999 to form a unified state, but little progress has been made in the ensuing two decades.
Meetings between Russian President Vladimir Putin and Lukashenka last year failed to bring the two sides together as the Belarusian president complained he was merely seeking "equal" terms.
Belarusian protests in December targeted the perceived secrecy of the talks and objected to closer ties to Russia.
Mike Pompeo this week postponed a planned visit to Minsk to meet with Lukashenka in what would have been the first visit by a U.S. secretary of state to that post-Soviet country in a quarter century.