Local authorities accused Ukraine of deliberately attacking civilians.
Ukraine did not immediately respond to a request for comment.
Both Russia and Ukraine deny targeting civilians in the war launched by Russia's full-scale invasion in February 2022.
Russian-appointed governor Yevgeny Balitsky said another 19 people had been wounded in the attack on the resort area of Kyrylivka, which lies on the coast of the Azov Sea near the town of Melitopol.
Russian foreign ministry spokeswoman Maria Zakharova said Ukrainian drones carried out the attack on "sleeping people" at the camp.
She denounced "inhuman crimes," also referring to an attack on a factory in Russia's Kirov region on Thursday which killed six people.
A video posted online of the holiday camp showed shattered buildings, burned-out cars and a pile of rubble next to a swimming pool.
Balitsky said crews from Russia's emergencies ministry had extracted two survivors, including a child, and recovered another body from the rubble.
He added that rescue operations had been completed.
"The enemy saw and understood who it was targeting," he said on the Telegram messaging app.
Ukraine said on Saturday its drones had hit a Russian oil platform in the Caspian Sea and an oil refinery in Siberia, while both Ukraine and Russia said they had struck ships carrying military cargo.
The energy targets lie 700km and 2000km from Ukrainian territory, underscoring the increasing reach of Ukraine's campaign to use long-range drones to undermine Russia's war effort and pressure the Kremlin to make peace.
Ukraine struck the Filanovsky oil platform belonging to Russia's Lukoil, its SBU security service said.
Lukoil did not immediately respond to a request for comment.
The platform is part of Russia's largest Caspian oil field.
Local authorities in the Siberian region of Tyumen confirmed that a Ukrainian drone had caused a fire at the region's refinery.
They did not say if output had been disrupted.
Both sides have increasingly targeted shipping as they seek to derail military logistics and supply lines far from the battlefield.
Elsewhere in the Caspian, Ukrainian drones attacked two cargo vessels - Port Olya 2 and Begey - believed to be involved in military cargo shipments between Russia and Iran, the SBU said.
Russia's transport ministry did not respond to a request for comment.
Russia and Iran have deepened military co-operation since Russia's 2022 invasion of Ukraine, with Iran supplying drones and drone technology that Russia has used extensively in the war, according to governments allied with Ukraine.
US Defense Secretary Pete Hegseth told lawmakers this week that Russian and Chinese authorities were supporting Iran in its war against the US in ways he would not specify.
However, President Donald Trump said he trusted both countries not to help Iran.
In the Black Sea, Russia's defence ministry said its drones had hit a bulk carrier delivering military cargo for the Ukrainian army.
In a separate daily report, the ministry said it had targeted Ukrainian logistics centres, production and storage sites for long-range drones, as well as energy, transport, and port infrastructure.
Ukrainian President Volodymyr Zelenskiy said in his nightly video address on Saturday that he expects North Korea to provide Russia with further troops and heavy weapons for its war against Ukraine.
Under a mutual defence pact, North Korea sent an estimated 14,000 soldiers to Russia's Kursk region in 2024 to help Russian soldiers beat back a major incursion into the region by Ukrainian forces.
Among other things, Zelenskiy insisted Russia was preparing to station 30,000 North Korean soldiers in the Russian region of Voronezh.
North Korea also intended to deliver additional launch pads for ballistic missiles to Russia, he said.
Zelenskiy said this was part of Russia's war planning for the coming northern hemisphere autumn.
