Russia has issued a thinly veiled threat against Belarus over the detention of 33 Russian mercenaries who were arrested at gunpoint near the capital, Minsk, last week.
Dmitry Medvedev, the deputy head of Russia's Security Council, said the incident could have grave consequences for bilateral relations.
His remarks came just days before Belarus holds a crucial presidential election in which longtime President Alyaksandr Lukashenka is seeking to extend his 26 years in office.
Medvedev said the Belarusian leadership had turned bilateral ties into "small change in the election campaign.”
"It's not only offensive, it's very sad,” said Medvedev, who previously served as Russian president and prime minister. "And it will entail sad consequences, too."
The mercenaries' arrest, and the circumstances of their presence in Belarus, has ratcheted up tensions in the run-up to the August 9 presidential vote.
Lukashenka is facing one of the most serious challenges to his tenure, with masses of Belarusians attending campaign rallies organized by his challengers.
Belarusian authorities have charged the arrested Russians with plotting to stage riots. Russia has demanded their release, saying they were only in Belarus because they missed a connecting flight to another country.
In a speech on August 4, Lukashenka lashed out at the Russian mercenaries, suggesting they were plotting a "colored revolution" in Belarus -- a reference to the popular upheavals that have rocked Georgia, Ukraine, and Kyrgyzstan over the past two decades.
The Russians were reportedly employed by a private military firm owned by Yevgeny Prigozhin, a Kremlin-connected businessman who has been indicted in the United States for meddling in the 2016 U.S. presidential election.