The Belarusian defense ministry says the country's troops have received training from members of Russia's Wagner private military group.
The ministry said on Friday that the session took place at a training ground southeast of the capital, Minsk.
It released footage that it says shows Wagner fighters giving Belarusian forces instructions. The fighters reportedly taught the Belarusians how to shoot and provide medical assistance.
The defense ministry said the Belarusian forces and the Wagner Group members have also developed a roadmap for future training sessions.
Belarusian President Alexander Lukashenko said that his country would accept Wagner fighters, after the mercenary group's leader Yevgeny Prigozhin led a short-lived mutiny in Russia.
Ukraine's President Volodymyr Zelenskyy said in a speech on Friday that he had received an "important report" on the situation in Belarus from an intelligence official.
Zelenskyy said, "We are closely monitoring what is happening there in terms of security." He added, "As of today, there are no large-scale threats."
The Ukrainian military is on alert against moves by the Russian ally. A Ukrainian commander said troops have laid about 5,800 mines at 30 locations along the northern border with Belarus over the past 10 days.