Ukraine’s air force shot down two Russian planes on Monday, it said, including a military spy plane.
Kyiv’s military chief said the downing of the two planes, an A-50 long range radar detection aircraft, and an Il-22 air control centre craft, was a significant blow to Russian air power.
The planes are key tools in helping orchestrate Russian battlefield movements in Ukraine.
Russia has largely ensured its air dominance during the war, as Ukraine fights with its fleet of Soviet-era warplanes against Moscow’s more modern aircraft.
General Valeriy Zaluzhnyi, the commander-in-chief of the Ukrainian armed forces, did not say how the planes were brought down, but Ukraine has received sophisticated air defence systems from its Western allies.
The planes appeared to have been downed above the Azov Sea, which lies between Ukraine and Russia, north of the Crimea Peninsula and the Black Sea.
There was no immediate official comment from Moscow.
Pro-Kremlin war bloggers claimed both planes had come under friendly fire, but presented no evidence of that.
The A-50, which is topped with a large radar, typically carries a crew of 15. The Russian air force reportedly has been operating a fleet of nine such aircraft.
A February 2023 drone attack at an airfield in Belarus damaged a parked A-50, but Russian and Belarusian officials described the damage as minor.
The Il-22 is an airborne command post. It oversees military operations and sends radio signals to troops on the front line. The Russian air force reportedly has a dozen such planes.
The news came as Ukrainian president Volodymyr Zelenskyy was due to meet Swiss President Viola Amherd in Bern later Monday before attending the World Economic Forum in Davos on Tuesday.
Ukrainian officials are striving to keep world attention on the war amid concerns that the conflict is slipping down the list of global priorities.
The UK at the weekend announced £2.5bn of military aid to Ukraine over the coming year.
It is the UK's largest annual commitment since Russia's full invasion of Ukraine in February 2022.