Russia's defence ministry said Ukraine used US-supplied weapons in the attack and accused it of using cluster munitions.

Sevastopol, a Black Sea port city and naval base on the Crimean peninsula annexed by Russia in 2014, regularly comes under fire from Ukraine but Sunday's attack was unusually deadly.

Sevastopol governor Mikhail Razvozhayev wrote on Telegram that two children and one adult had died. "The number of wounded has risen almost to 100 people," he added.

The governor said Ukraine had launched five missiles which Russian air defences intercepted over the sea but fragments fell onto the shore area and shrapnel wounded people.

Razvozhayev said missile fragments hit beach areas in the north of the city and set fire to a house and woodland.

A Russian defence ministry statement said Ukraine committed a "terrorist attack on civilian infrastructure of Sevastopol with US-supplied ATACMS tactical missiles loaded with cluster warheads".

The ministry said four missiles were downed and a fifth changed trajectory after being intercepted "with its warhead exploding in the air over the city".

A local news channel on Telegram, ChP Sevastopol, cited witnesses as saying that an elderly woman was killed as she swam in the sea.

Earlier, a drone launched by Ukraine on Russia's southern Belgorod region killed a man, the governor said.

Three Ukrainian attack drones struck the town of Graivoron, near the border with Ukraine, said Belgorod governor Vyacheslav Gladkov, with one hitting a car park near a multi-storey block of flats.

"A peaceful civilian was killed. The man died from his wounds at the spot" and three people were wounded, Gladkov wrote on Telegram.

Ukrainian President Volodymyr Zelensky in a social media post Sunday urged supporter countries to help Ukraine step up attacks on Russian soil.

"We have enough determination to destroy terrorists on their territory - it is only fair -- and we need the same determination from our partners. We can stop Russia," Zelensky wrote.

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