Moscow shooting poses awkward questions for Russia's intelligence agencies

The FSB has said Friday's concert hall attack was "painstakingly" planned and that the gunmen had carefully hidden their weapons.

Russian President Vladimir Putin lights a candle to commemorate victims of an attack on the Crocus City Hall concert venue, on the day of national mourning, in Russia. Picture: Mikhail Metzel, Sputnik, Kremlin Pool Photo via AP

Russia's security state has been ruthlessly effective at detaining Vladimir Putin's opponents but was caught off guard by a mass shooting near Moscow, raising questions about its priorities, resources and intelligence gathering.

Charged with hunting down Ukrainian saboteurs inside Russia, with keeping anti-Kremlin activists in check, and with disrupting the operations of hostile foreign intelligence agencies, the FSB, the main successor agency to the Soviet-era KGB, has its hands full.