Kyiv's military said its forces supported by military intelligence units have "destroyed" the Russian ship, the Caesar Kunikov, in the Black Sea.
"It was in Ukrainian territorial waters near Alupka at the time of the hit," the military posted on the messaging app Telegram.
The targeted vessel, described as "a large Russian landing ship," took part in Russian military operations in Georgia in 2008.
An earlier report from local media outlet Ukrainska Pravda said sea drones had struck and damaged a ship off the Crimean Peninsula.
The news organization's website showed several videos of a column of smoke over the sea off the southern coast of Crimea, with helicopters also seen flying over the area.
Meanwhile, Moscow said it had intercepted six Ukrainian drones over the Black Sea, which has become a key battleground in the war, with Kyiv's forces having escalated attacks there more recently.
Ukrainian cruise missiles hit a large Russian landing warship in Crimea in December, killing at least one
Russian missile attacks kill 3 in Donetsk region
Ukrainian officials say Russia launched an overnight missile attack on the town of Selydove in the eastern Donetsk region, killing three people and injuring about a dozen.
A hospital and several apartments were damaged, they added.
One of the dead was a child, the city's military administration said on the Telegram messaging app.
The Donetsk region's Governor Vadym Filashkin also posted on Telegram that 100 patients had to be evacuated to hospitals in nearby towns after the bombardment hit a wing of the town's hospital.
He posted footage of blown-out windows, ripped-apart walls, and rubble inside an apparent medical facility, where patients were sitting or lying in beds.
Filashkin said another strike had blown up several apartments in a medium-sized residential building and that at least four people had been injured.
Russia and Ukraine have denied targeting civilians in attacks on each other's territories, claiming that their goal is to destroy important military, power, and transport infrastructure.
Ukraine's new army head Syrskyi visits front line
Thenewly appointed head of the Ukrainian military, Oleksandr Syrskyi, has described the situation on the front line as precarious after a visit to the eastern combat zone.
Russian forces in the Donetsk region have been pressing to capture the town of Avdiivka and have poured huge resources and troops into the operation for incremental gains.
"The operational environment is extremely complex and stressful. The Russian occupiers continue to increase their efforts and have a numerical advantage in personnel," Syrsky said in a statement.
"We are doing everything possible to prevent the enemy from advancing deep into our territory and to hold the occupied positions," he added.
The Donetsk region of Ukraine has seen the worst fighting of the nearly two-year invasion.
Syrsky said he and Defense Minister Rustem Umerov had also visited Ukrainian forces further north, near the town of Kupiansk. Moscow's forces there have been trying to dislodge Ukrainian troops from their positions, and Kyiv is looking for new ways to bolster its defenses there.
"Based on the results of the work, a number of important decisions were made aimed at strengthening the combat capabilities of our military units and preventing enemy actions," Syrsky said, without elaborating.
Syrskyi, who has led Ukraine's ground forces since 2019, was promoted to replace Valeriy Zaluzhnyi as commander of the armed forces last week as the war with Russia approaches its third year.
