Russia has deployed its advanced S-400 air defense missile system to annexed Crimea, Russian news agencies reported on Friday

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 Defense 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.

The ministry had earlier in the day announced that its navy would start to hold three-day military exercises in the Black Sea to practice repelling underwater attacks by saboteurs.

Russia's Black Sea Fleet based in Crimea is taking part in the military exercises. More than 10 warships, MI-8 and Ka-27PS helicopters are participating in the training.

“During the drill we are going to practice the issues of both operational and technical support. These include operations to counter underwater sabotage, navigational and hydrographic exercise, search and rescue missions,” said Russian Navy Commander Admiral Viktor Chirkov.

Meanwhile, Russian Prime Minister Dmitry Medvedev said on Friday that Moscow could break diplomatic relations with Kiev over the security incidents in Crimea.

Russian state news agencies quoted the prime minister as saying that he is not interested in severing the ties, but "if there is no other way to change the situation, the president could take this step."