Russia has deployed its advanced S-400 air defense missile system to annexed Crimea, Russian news agencies reported on Friday, citing a statement from the Russian Defence Ministry.

The announcement comes two days after President Vladimir Putin promised to take counter-measures after what he said were clashes between Russian forces and Ukrainian saboteurs in northern Crimea.

Ukraine denies the clashes took place. Russia annexed Crimea from Ukraine in 2014, Reuters reports.

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