Poland summoned Russia's ambassador on Wednesday over an incident involving a Russian fighter jet and Polish border guard aircraft over the Black Sea early in May, a spokesperson for the Polish foreign ministry said.
The near-miss incident put Nato's air policing units in a higher state of readiness and worsened already-hostile relations between Russia and Poland, which has been a strong supporter of Ukraine as it battles a Russian invasion.
The incident on 7 May occurred when a Polish border guard aircraft, on patrol for the European Union's border agency Frontex, narrowly avoided a collision with a Russian fighter jet over the Black Sea, Romania and Poland have said.
"We strongly condemn the provocative and aggressive behaviour of the Russian side, which is a serious international incident," ministry spokesperson Lukasz Jasina wrote on Twitter.
The Russian embassy in Warsaw was not immediately available for comment.
The Russian ambassador was summoned to Poland's foreign ministry earlier this month over a statement made by the former ombudsman for Russian children calling for the murder of the Polish ambassador.