Poland said on Tuesday it was rushing troops to its eastern border after accusing Belarus, Russia's closest ally, of violating its airspace with military helicopters.
The Belarusian military denied any such violation and accused NATO member Poland, one of Ukraine's most fervent backers in its conflict with Russia, of making up the accusation to justify a buildup of its troops.
Belarus leader Alexander Lukashenko had earlier taunted Poland over the presence of Russian Wagner mercenaries near their joint border.
Poland's Defence Ministry said it was sending "additional forces and resources, including combat helicopters". It said it had informed NATO of the border violation and Belarus' charge d'affaires had been summoned to provide an explanation.
The Polish military initially denied any border violation had occurred but later, after consultations, said the intrusion took place "at a very low height, hard to intercept by radar".
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