President Volodymyr Zelenskyy has given Belarus's leader a week to remove equipment from his country used in Russian drone attacks on Ukraine.
The Ukrainian leader has threatened to take action if his message is ignored.
President Alexander Lukashenko, who has been in power for decades, said recently that Ukraine had nothing to fear from Belarus and dismissed any notion that his country would get involved in the war.
But speaking on Friday, Mr Zelenskyy said signal relay stations were located in two Belarusian regions that border Ukraine, used by Russian forces to help drones navigate during attacks on Ukrainian civilians.
"What's the point of saying he (Lukashenko) doesn't want to be in the war? Let him remove this equipment, let him switch it off," he said.
"I think a week will be enough for him to do that."
"If he doesn't do it, we'll do it," he added, without elaborating.
Mr Lukashenko, a key ally of President Vladimir Putin, allowed Russian forces to use Belarusian territory to launch attacks when they launched the full-scale invasion in 2022.
Read more from Sky News:
Ukraine could have fresh hope of US support
There has been some recent indications that ties between the US and Belarus may be improving.
Meanwhile, a spat between Mr Zelenskyy and Poland's Karol Nawrocki has continued.
The Polish president has decided to strip the Ukrainian leader of Poland's top honour after he renamed an army unit after the Ukrainian Insurgent Army, nationalists who massacred Poles during the Second World War.
Mr Zelenskyy responded by sharing an image of the medal apparently being returned to Poland in the post.
(c) Sky News 2026: Ukraine gives Belarus ultimatum over Russian drone equipment
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