Kyiv will be ready if Belarus's armed forces join Russia's war effort in Ukraine, a spokesperson for the Ukrainian State Border Service said on Wednesday.
Belarus, a close ally of Russia, said its military had begun large-scale drills on Wednesday to test their combat readiness and that they posed no threat to its neighbours.
"We do not rule out that the Russian Federation could at some point use the territory of Belarus, the Armed Forces of the Republic of Belarus, against Ukraine," said Andriy Demchenko, spokesperson for Ukraine's State Border Service.
"Therefore, we are ready," he said, adding that the border with Belarus had been strengthened since Russia invaded Ukraine on Feb. 24.
Russia launched the invasion after holding joint drills with Belarus which had allowed it to move more forces closer to the border with Ukraine.
Areas of Ukraine adjacent to Belarus came under Russian assault in the initial stage of the invasion but Russian attacks are now focused on Ukraine's eastern and southeastern regions.
Demchenko said Ukraine had also reinforced its border with the Russia-backed region of Transdniestria, where tensions have been rising since local authorities said it was subject to a series of attacks.
Ukrainian officials have expressed concern about the situation in Transdniestria, and condemned what it said were Russian attempts to drag the region into Russia's war against Ukraine. Moscow has also voiced concern and said it is following events in Transdniestria closely.
Kent Logsdon, the U.S. ambassador to Moldova, said on Wednesday Russia's invasion of Ukraine and what he described as its attempts to redraw the map of Europe at gunpoint were a cause of great concern around the world.
But he told a conference in Moldova that Washington had no evidence that Moscow wanted to extend the war to Moldova and said Russian President Vladimir Putin would lose the war, Moldovan media reported.
(Reporting by Natalia Zinets, additional reporting by Alexander Tanas in Chisinau, Editing by Timothy Heritage)