The Russian Navy has held exercises in the Black Sea.
The drill took place in Sevastopol Bay on Thursday.
Officials say the aim is to practice repelling underwater attacks by saboteurs.
The attack involved:
Russian Little Rook anti-saboteur boats
Raptor patrol speed boats
Naval Ka-27 and MI-8 helicopters
400 military personnel
10 military vehicles
The situation in eastern Ukraine and Crimea has deteriorated over the last few days.
Russia has stepped up military exercises in the region.
Russia annexed Crimea from Ukraine after a referendum in March 2014.
A conflict between Russian-backed separatists and Ukrainian forces flared up in eastern Ukraine weeks later and is ongoing.
Pro-Russian separatists are fighting the Kyiv government’s forces in the eastern Ukraine region, despite a fragile ceasefire.
The UN’s human rights chief says civilian casualties from shelling, mines and booby traps in eastern Ukraine are at their highest in a year.
A peace plan for the eastern Donbass region of Ukraine was negotiated by Minsk between Ukraine and Russia by Germany and France 18 months ago.
It has been stalled for months.
The Russian view
On Wednesday, the Russian President accused Ukraine of using terrorist tactics to try to provoke a new conflict and destabilise the contested peninsula.
Vladimir Putin’s claim came after the Russian Security Service (FSB) said they, together with military units, had aborted an attempt by alleged Ukrainian saboteurs to infiltrate Crimea.
Russia’s Ambassador to the UN, Vitaly Churkin, has dismissed concerns about Moscow’s military build-up.
The Ukrainian view
Ukraine has strongly rejected Russia’s allegations about Crimea.
Kyiv says it would never try to return the territory by military force.
Ukrainian President Petro Poroshenko has described Vladimir Putin’s claims as “fantasies”.
Ukraine’s UN envoy, Ambassador Volodymyr Yelchenko, says a debate has been held behind closed doors at the Security Council in New York:
“My biggest hope is that the discussion in the UN Security Council will help the Russian Federation understand that they cannot really continue with this kind of behaviour.”
“The troops in the area are not a coincidence. These numbers may reflect some very bad intentions and this is the last thing we would like to happen.”
What they are saying
“These drills include operations to counter underwater sabotage, navigational and hydrographic exercise, search and rescue missions etc. Judging by today’s outcome, one can say the military personnel are well-trained,” – Russian Navy Commander-in-Chief Admiral Vladimir Korolev says Moscow’s drill is part of the broader exercise “Caucasus 2016.