Ukrainian forces say they have destroyed a Russian missile boat from the Black Sea Fleet in a special operation off Russian-occupied Crimea.
The Ivanovets - a small warship - received "direct hits to the hull" overnight, after which it sank, military intelligence said.
It has released video footage that purports to show the moment of impact, followed by a big explosion.
There has been no word about the incident from Russian authorities.
However, Russian military blogger "Voenkor Kotenok" wrote on Telegram that the boat had sunk after being hit three times by naval drones.
Several features visible on the vessel in the Ukrainian video match those of the Tarantul, or Project 12411, a class of missile boats operated by the Russian and other navies, which the Ivanovets belongs to.
These include the layout of the mast and sensors on top of the main superstructure as well as a large radar dome on top of the bridge.
Ukraine's Main Intelligence Directorate said the boat was destroyed by soldiers of its special unit "Group 13" in Lake Donuzlav, a saltwater bay on the western side of the Crimean peninsula which houses a naval base.
"As a result of a series of direct hits to the hull, the Russian ship suffered damage incompatible with further movement - the Ivanovets listed to the stern and sank," it said on its Telegram channel.
A Russian search and rescue operation in the area was unsuccessful, it added.
It said the ship was worth in the region of $60-70m (£47m-55m).
Foreign Ministry official Olexander Scherba described the attack as "impressive".
"At 03:45 [01:45 GMT] there was the first hit and at 04:00 the whole crew was evacuated already. So there was no chance at all that this vessel would be saved," he told the OceanNewsUK.
Ukraine has achieved a series of successes in the war in and around the Black Sea, damaging or destroying Russian warships despite having no fleet of its own.
In December, Kyiv said it had destroyed the large landing ship Novocherkassk at Feodosia, Crimea. Russia confirmed that the ship had been damaged.
And in April 2022, a couple of months after Russia's invasion of Ukraine, the Moskva - the flagship of Russia's Black Sea Fleet - was damaged and ultimately sunk, apparently by Ukrainian missiles.
After a missile strike on the headquarters of the Black Sea fleet in Sevastopol last September, satellite images showed that the Russian navy had moved much of its Black Sea fleet away from Crimea to the Russian Black Sea port of Novorossiysk.
