Russia has said it plans to deploy new missiles to Crimea as tensions rise with Ukraine over Moscow's seizure of three navy ships and their crews.
New military hardware has steadily been poured into Crimea by Russia since it annexed it from Ukraine in 2014.
However, the long-simmering tensions between the two countries escalated on Sunday when Russia was accused of opening fire on Ukrainian ships, three of which were taken into Russian custody along with their crews.
Moscow's announcement about a further deployment of advanced S-400 surface-to-air missile systems comes as it and Kiev try to pin the blame on each other for the confrontation.
A Reuters correspondent in Crimea on Wednesday also observed a Russian navy minesweeper ship, the Vice-Admiral Zakharin, heading for the Sea of Azov, which is used by both Ukraine and Russia and is an area of growing tensions, from the Black Sea.
Russian news agencies cited Vadim Astafyev, a spokesman for Russia's southern military district, as saying that a new battalion of S-400 missiles would be delivered to Crimea soon and become operational by the end of the year.
The missile deployment is likely to have been long-planned, but the timing of the announcement appeared designed to send a message to Ukraine and the West that Russia is serious about defending what it regards as its own territory and waters.
Crimea already hosts three battalions of the anti-aircraft missile systems which have a range of up to 400km, allowing Russia to control large swathes of the skies above the Black Sea.
The announcement comes after a dramatic recording suggested a Russian military ship was ordered to “squash” a Ukrainian boat in a maritime clash. The footage appeared to show one of their ships deliberately ploughing into the much smaller Ukrainian vessel.
In the video a man can be heard shouting: “Squash him, well done, squeeze him from the right...”
According to Ukrainian sources, six of its naval crew were wounded and 24 were detained after the Russians opened fire on the boats and seized two armoured ships and a tug.
Russia has alleged Ukraine orchestrated the incident to boost the poll ratings of president Poroshenko in coming elections.
A Crimean court was due to order the detention of nine of the captured Ukrainian sailors - including senior Ukrainian naval officers and at least one member of Ukraine's SBU intelligence agency - later on Wednesday
A court in Simferopol, the capital of Crimea, on Tuesday ordered the other 15 Ukrainian sailors to be detained for two months pending a possible trial.
All of the sailors face jail terms of up to six years if found guilty of what Moscow says was a plot to illegally cross the Russian border by trying to pass through the Russian-controlled Kerch Strait on Sunday without advance notice and ignoring calls to stop.
Ukraine says its ships did nothing wrong and have every right to use the strait, the only gateway to the Sea of Azov from the Black Sea, without Russian permission.
Additional reporting by Reuters.
