The Belarusian defense ministry said on Sunday it had summoned Ukraine's military attaché to protest against what it called repeated violations of Belarus' airspace by Ukrainian aircraft.
Relations between the two countries have plummeted since last year, when Russia sided with Belarusian President Alexander Lukashenko during mass street protests and Lukashenko in turn became more vocal in his support for Moscow against Ukraine.
Belarus handed a note of protest to the Ukrainian official, the ministry said in a statement.
"The military attaché was informed that the Ukrainian side is avoiding a dialogue to resolve disputes ... which is very worrying," the ministry said.
Belarus said on Saturday that a Ukrainian military helicopter had flown one km (0.6 miles) into Belarusian territory during maneuvers. A spokesperson for Ukraine's border guard service denied the accusation.
The Ukrainian army said on Sunday that it had nothing to add to that comment.
"Maybe someone made a mistake and is spreading accusations for manipulative purposes," a spokesperson said.
Russian President Vladimir Putin and US President Joe Biden are due to hold a video call on Tuesday where they will discuss wider tensions in the region.
Ukraine and its NATO allies accuse Russia of massing tens of thousands of troops near Ukraine's borders in what they say might be preparation for an attack. Russia denies any such plan.