The Kremlin said Thursday that the Crimean peninsula it annexed in 2014 was vulnerable to Ukrainian attacks after officials there said they had shot down a drone near a key naval base.
The latest drone attack comes after Russian President Vladimir Putin recently visited the only bridge connecting Crimea with the Russian mainland to survey work to repair the key artery in the wake of a blast.
"There are certainly risks because the Ukrainian side continues its policy of organising terrorist attacks. But, on the other hand, information we get indicates that effective countermeasures are being taken," Kremlin spokesman Dmitry Peskov told reporters.
The Moscow-appointed governor of Crimea Sergei Aksyonov said last month that Russia was strengthening fortifications on the peninsula in the wake of recent attacks.
And the governors of two Russian regions bordering Ukraine have said they inspected the construction of defence lines days after Ukrainian drones struck key military airfields.
In the latest incident over Crimea on Thursday, Russia said it had shot down a drone over the Black Sea near Sevastopol, the largest city on the Crimean peninsula that hosts a key Russian naval base.
"As per usual our military carried out its work well," said the governor of the Sevastopol administrative region, Mikhail Razvozhayev.
The peninsula was annexed by Russia in 2014 after a so-called referendum that Ukraine and the West never recognised.
The Russian military used Crimea as one of its lauching pads for its military intervention in Ukraine on February 24 and it has been regularly attacked by drones.
There have been several explosions at or near Russian military installations in Crimea since February, including a coordinated drone attack on a key Russian naval port at Sevastopol.
In October, the Kerch bridge linking the peninsula to the Russian mainland was partially destroyed in an attack attributed to Ukraine by Moscow.
The shooting down of the drone on Thursday came after a series of attacks deep in Russia -- including the Engels airfield, a strategic bomber military base -- for which Ukraine has not claimed responsibility.
Separately, the Russian security services (FSB) arrested two people accused of spying for Ukraine on Crimea and accused them of "treason," the agency's press service said Thursday.
The FSB "halted the illegal activities of two Russian citizens suspected of committing high treason in the form of spying in the interests of the Security Service of Ukraine," it said in a statement.
One of those detained is "a supporter of Ukrainian nationalist ideology and was recruited by the Ukrainian secret services in 2016," the statement said.
He is suspected of "transferring data on the location of Russia's defence ministry facilities to a foreign security agency, which could be used against Russia's security."
