A senior official in Russian-annexed Crimea accused Ukraine on Sunday of carrying out a drone attack ahead of planned celebrations to mark Navy Day, injuring five and forcing the cancellation of festivities.
The accusation comes hours before Russian President Vladimir Putin is due to oversee Navy Day celebrations in his hometown of St Petersburg and approve Russia's naval doctrine as Moscow presses on with its military intervention in Ukraine.
"An unidentified object flew into the courtyard of the fleet's headquarters," Mikhail Razvozhayev, governor of Sevastopol, home to Russia's Black Sea fleet, wrote on the Telegram messaging app.
"According to preliminary information, it is a drone."
He said Ukraine had decided to "spoil Navy Day for us".
The Ukrainian defence ministry did not immediately respond to a request for comment.
Razvozhayev said that five employees of the fleet headquarters had been injured in the incident and that the Federal Security Service (FSB) was investigating its circumstances.
"All celebrations have been cancelled for security reasons," Razvozhayev said. "Please remain calm and stay home if possible."
Navy Day is an annual Russian holiday during which its fleets stage naval parades and honour its sailors.
Russia annexed Crimea from Ukraine in March 2014, prompting a major row with the West which deepened over Moscow's role in an insurgency of pro-Russian separatists in eastern Ukraine.