Vessels from Russia's Black Sea Fleet have taken up position near the disputed Crimean peninsula - which was illegally annexed from Ukraine in 2014 - to help strengthen the air defences.
The aggressive land grab plunged Ukraine-Russia and east-west relations to their lowest point in years and threatened a new Cold War.
Kiev began two days of missile tests today, angering Russia, which has put its air defence forces on high alert.
Moscow has warned that the war games will not disrupt international flights.
The drills come more than two years after a Malaysia Airlines jet was downed over Ukraine during fighting with Russian-backed separatist rebels.
A military source in Crimea told the Reuters news agency: “Warships of the Black Sea Fleet have taken up positions near Crimea's western coast for the duration of Ukraine's planned missile tests from December 1-2.
“The ship's air defence units have been put on a higher state of alert.
“Their equipment is designed in the first instance to shoot down heavy anti-ship missiles and cruise missiles.
"Together with land-based air defence units on the peninsula, the ships have thrown up a practically impenetrable shield against the enemy's rockets.”
Vladimir Krizhanovsky, a Ukrainian military official, earlier said that the exercises had begun and that everything was going smoothly.
He said: “The tests are being carried out in accordance with international law.”
He said they were taking place at least 18.64 miles from Crimean air space.
