A Russian aircraft performed "aggressive manoueuvres" against a Polish fighter jet over the Black Sea, causing it to lose control.
The Polish border force said the Russian Sukhoi Su-35 didn't make radio contact as it approached the border guard plane three times.
It failed to keep to the "required safety distance", the agency added.
The Polish L-410 Turbolet ran into turbulence before the crew "lost control of the aircraft" and began to plummet.
At one point, the Russian fighter flew "around five metres" away from the nose of the Polish aircraft.
A spokesman for the government in Warsaw Piotr Muller branded the incident a "planned provocation by Russia."
He told Polish TV: "We can see that Russia is trying to draw international attention by such provocations."
The aerial spat was first reported on Friday by Romania's defence ministry, which slammed Moscow for its "aggressive and dangerous behaviour", adding that it was "completely unacceptable".
"This incident is further evidence of the provocative approach of the Russian Federation in the Black Sea," it said.
The incident happened in "international airspace over the Black Sea, around 37 miles east of Romanian airspace, its defence ministry said.
The air forces of Spain and Romania were put on "pre-alert".
The Polish aircraft managed to land safely in Romania shortly after the incident.
"The crew, including mainly two pilots, showed excellent skills and especially great composure, thanks to which they managed to land safely," Poland's border force said.
Just one week ago, Russian fighter jets dumped fuel on a US Reper drone and then smashed into it while in the air.
It comes as it emerged that Ukraine's air defences had shot down 35 Iranian-made drones over Kyiv during Russia's latest nighttime assault.
The bombardments came as Moscow enforced tight security on the eve of traditional Red Square commemorations marking the defeat of Nazi Germany in World War II.
Russian media counted at least 21 Russian cities that canceled military parades - the staple of Victory Day celebrations across Russia - on May 9 for the first time in years. Regional officials cited "security concerns" or vaguely referred to "the current situation".
Parades will go ahead in Russia's largest cities, Moscow and St. Petersburg. But the use of drones has been banned in both cities ahead of Victory Day.
In St. Petersburg, which is often referred to as "northern Venice" for its network of rivers and canals, using jet skis in certain parts of the city has also been prohibited until May 10.
In the Russian capital, car-sharing services have been temporarily barred from the city center - drivers will not be able to start or finish rides there.
Five people in the capital were injured by falling drone debris, according to Serhii Popko, head of the Kyiv City Military Administration. Air raid alarms sounded for more than three hours during the night.
Drone wreckage struck a two-story apartment building in Kyiv's western Svyatoshynskyi district, while other debris struck a car parked nearby, setting it on fire, Kyiv Mayor Vitali Klitschko said in a Telegram post.
Facing economic sanctions and limits on its supply chains due to its invasion of Ukraine in February 2022, Russia has routinely turned to Iranian Shahed drones to bolster its firepower.
Russian shelling of 127 targets across northern, southern and eastern parts of Ukraine killed three civilians, the Ukrainian defense ministry said.
The Kremlin's forces used tanks, drones, mortars, warplanes, multiple rocket launchers and surface-to-air missiles to bombard Ukraine, the report said.
Russian long-range bombers launched up to eight cruise missiles at Ukraine's southern Odesa region, authorities said. One person was killed and three wounded.
Some of the Soviet-era cruise missiles fired against the Odesa region self-destructed or fell into the sea before reaching their targets, according to Ukrainian air force spokesman Yuri Ihnat.
In addition, six Russian rockets also struck the eastern Ukrainian city of Kramatorsk during the night, a regional official reported Monday.
The missiles targeted the city's industrial zone and caused no casualties, Donetsk regional governor Petro Kyrylenko said in a Telegram post.
