The agency characterised it as the world's first downing of a combat plane by a maritime drone.
Its statement on social media said the fighter had been shot down by a military intelligence unit called Group 13 on Friday over waters near Novorossiisk, a major Russian port city on the Black Sea.
Outmanned and outgunned by its larger, wealthier Russian adversary, Ukraine has turned to drone warfare in the air and at sea as a way to fight back throughout more than three years of full-scale war.
Ukraine's seaborne drones, which are much cheaper and smaller than conventional ships, have wrought havoc on Russia's Black Sea fleet.
Ukraine has previously said it shot down a Russian military helicopter in December 2024 using a missile fired from the same type of seaborne drone.
The Russian Defence Ministry did not comment on the Ukrainian claim, but an authoritative Russian blogger believed to be close to the ministry said the jet had been shot down.
"Yesterday, towards evening, a Su-30 naval aviation fighter jet was shot down by the Ukrainian side 50 kilometres west of Novorossiisk. This was done from an uncrewed boat with an R-73 SAM (surface-to-air missile)," the blogger, who goes by the name Rybar, wrote on the Telegram messaging app.
"The pilots ejected and were picked up by civilian sailors. Both are alive, and to hell with the plane."
The mayor of Novorossiisk declared a state of emergency on Saturday after local authorities said a Ukrainian drone attack had damaged a grain terminal and several residential buildings, injuring five people.Â
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