The RIA Novosti news agency reported it would be in place by the end of the year, joining three other S-400 systems already on the peninsula, which Russia annexed from Ukraine in 2014.

"In the near future, a new anti-aircraft system will take up combat duty to protect the airspace of the Russian Federation," Colonel Vadim Astafiyev of Russia's southern military district told news agency Interfax.

He told the news agency the new S-400 system for Crimea had undergone successful testing and was ready to be deployed.

Sources in Russian security services had said in September that a fourth system would be deployed in Crimea near Dzhankoy, a town close to Ukrainian-controlled territory.

Wednesday's announcement came with Moscow and Kiev embroiled in their biggest crisis in years, after Russian border patrol boats seized three Ukrainian naval vessels off the coast of Crimea on Sunday.

The S-400 "Triumph" is Russia's latest and most advanced anti-aircraft and missile defence system.