There was no immediate comment from Ukraine, which like Russia, says it does not deliberately target civilians in the full-scale war which the Kremlin launched in 2022.
Social media videos, verified by Reuters, showed what appears to be a drone slamming into a busy beach area near the town of Gelendzhik, accompanied by a loud explosion.
Veniamin Kondratyev, the governor of Russia's southern Krasnodar region where Gelendzhik is located, called what had happened a tragedy.
He said 17 people were being rushed to hospital.
"What happened today was a deliberate attack by the Kyiv regime on the civilian population, which has no connection whatsoever to military infrastructure," Veniamin Kondratyev, the governor of Russia's southern Krasnodar region which includes the resort, said in a statement on Telegram.
A specialist medical disaster team had been dispatched to the scene of the explosion at the holiday village of Arkhipo-Osipovka, part of the wider Gelendzhik resort area, local authorities said.
Russian foreign ministry spokeswoman Maria Zakharova was cited by the TASS state news agency as accusing Ukraine of resorting to terrorism.
Russia last month accused Ukrainian forces of killing 11 people, including four children, in an attack on a holiday camp in a Russian-held part of Ukraine's Zaporizhzhia region.
Russia itself has repeatedly struck targets in Kyiv and other Ukrainian cities, displacing millions and laying waste to swathes of Ukraine.
Thousands of civilians have so far died in the war, most of them Ukrainians killed in Russian attacks.
Ukraine has been defending itself against Russia's full-scale invasion for more than four years with substantial military and financial support from its allies.
Ukraine has stepped up long-range attacks deep into Russia in recent months, mainly targeting oil refineries and e-commerce warehouses, in what it says is a campaign to make Russian citizens feel the cost of the war.
Meanwhile, Ukrainian President Volodymyr Zelenskiy appointed chief negotiator Rustem Umerov as the new head of the foreign intelligence service on Monday.
Umerov, who had previously served as defence minister among other roles, will remain responsible in his new role for the negotiations with Russia, which were most recently conducted under US mediation, Zelenskiy said.
Umerov, who was most recently secretary of the National Security Council, is also to co-ordinate the export of Ukrainian drones and their integration into the defence systems of other countries, Zelenskiy said during a meeting with diplomats.
According to the report, contracts are now in place with nine countries, with further agreements planned.
with DPA
