* This content was produced in Russia where the law restricts coverage of Russian military operations in Ukraine (Recasts with "Judgement Day" attack quote)
MOSCOW, July 17 (Reuters) - The refusal of Ukraine and Western powers to recognise Moscow's control of Crimea poses a "systemic threat" for Russia and any outside attack on the region will prompt a "Judgment Day" response, former president Dmitry Medvedev said on Sunday.
Russia annexed the Black Sea peninsula of Crimea from Ukraine in 2014 after a pro-Moscow president in Kyiv was toppled amid mass street protests. Moscow then also backed pro-Russian armed separatists in the Donbas region of eastern Ukraine.
In the event of an attack on Crimea, Medvedev was quoted by TASS news agency as saying, "Judgment Day will come very fast and hard. It will be very difficult to hide."
Medvedev did not elaborate but has previously warned the United States of the dangers of attempting to punish a nuclear power such as Russia over its actions in Ukraine, saying this could endanger humanity.
His comments were aired a day after a Ukrainian official suggested that Crimea, which most of the world still recognises as part of Ukraine, could be a target for U.S.-made HIMARS missiles, recently deployed by Kyiv as it battles Russian forces.
Earlier on Sunday, Interfax news agency quoted Medvedev as telling World War Two veterans: "If any other state, be it Ukraine or NATO countries, believes that Crimea is not Russian, then this is a systemic threat for us."
"This is a direct and an explicit threat, especially given what had happened to Crimea. Crimea returned to Russia," said Medvedev, who now serves as deputy chairman of the Russian Security Council.
Vadym Skibitskyi, an official at Ukrainian military intelligence, was asked on Saturday in a televised interview if HIMARS could be used on targets in Crimea.
He said Russia had carried out strikes on Ukrainian territory from Crimea and the Black Sea and so these were also justified targets.
Crimea is of particular strategic importance to Russia as it includes the headquarters of its Black Sea fleet at Sevastopol. (Reporting by Reuters Editing by Guy Faulconbridge and Gareth Jones)