Kyiv has accused Minsk of preparing to send its own troops into Ukraine following Russia's invasion.
Belarus says it has expelled the majority of Ukrainian diplomats based in the country due to "unfriendly" actions.
Belarusian foreign ministry spokesman Anatoli Glaz accused Kyiv on Wednesday of "interfering" in state affairs.
"Belarus has decided to reduce the number of Ukrainian diplomats on its territory," he announced on Wednesday.
"This measure is aimed at ending non-diplomatic activities of a number of staff members of Ukrainian diplomatic institutions."
Of more than 20 embassy staff, only the Ukrainian ambassador and four diplomats will remain in Minsk, he added.
Belarus said it will also close the Ukrainian consulate in Brest "due to the effective absence of staff".
Minsk -- a key ally of Russia amid the war in Ukraine -- had already withdrawn all its own diplomats from Ukraine.
"Since 2020, Belarus has observed numerous unfriendly actions of Ukraine aimed at the irresponsible destruction of interstate relations with our country, trade contacts and long-established ties," Glaz said.
"The situation has reached such a point that the Ukrainian authorities have started to interfere directly and indirectly in our internal affairs and put contacts between our states on hold."
As early as 2021, they called Belarus an enemy country," he added.
On Tuesday the Belarusian security service, the KGB, accused eight Ukrainian diplomats of espionage.
Meanwhile, Ukrainian officials have repeatedly accused Minsk of preparing to send its own troops into Ukraine, which Belarus denies.
The country has also served as a platform for the first two sessions of Russian-Ukrainian talks.
Ukraine's foreign ministry said on Thursday it had told Belarus to cut its diplomatic staff in Kyiv to five people in response to Minsk's move.
"We caution the Belarusian authorities that any further unfriendly steps towards Ukraine will receive a decisive response," a statement read.