Russian President Vladimir Putin suddenly sacked Moscow's ambassador to Belarus, Mikhail Babich, the Kremlin said on Tuesday, amid a row over contaminated oil and a wider political discord between the ex-Soviet countries.
Belarussian President Alexander Lukashenko has generally been more closely aligned with Moscow than any other ex-Soviet leader, while the lack of tolerance for dissent at home has made him largely a pariah in the West.
However, Minsk has shown increasing signs of seeking a thaw with the United States and the European Union since 2014, when Belarus did not recognise Russia's annexation of the Crimea peninsula from neighbouring Ukraine.
Lukashenko has said Russian officials had sometimes set unacceptable conditions for Belarus, such as adopting the Russian currency or even merging with Russia.
Babich had been appointed Moscow's envoy to Belarus last August. He had criticized Belarus authorities amid the row over oil tax change which Belarus says will cost its budget $400 million this year.
The Kremlin said on Tuesday Babich will move to another job and will be replaced by Dmitry Mezentsev, a lawmaker from the upper house of parliament.
The wider political differences have been exacerbated by the contaminated Russian oil flows to European countries including Belarus.