As Ukraine and the United States launched joint naval exercises in the Black Sea on Monday, Russia reportedly tested the readiness of its air defence systems in Crimea.
The "Sea Breeze" excercise comes just days after the British navy's HMS Defender passed near Russian-annexed Crimea in the Black Sea, with Moscow saying it fired warning shots at the destroyer to ward it off.
The Sea Breeze drills -- which have taken place 21 times since 1997 -- will involve some 5,000 military personnel from more than 30 countries.
Russia on its part deployed about 20 warplanes and helicopters, including Su-24M bombers, as well as S-400, according to Interfax news agency.
'Powerful message to maintain stability and peace in our region'
Ukrainian navy commander Oleksiy Neizhpapa said during an opening ceremony in Odessa that the exercises would send a "powerful message to maintain stability and peace in our region."
Russia denounced "the scale and aggressiveness" of the drills which "hardly contribute to security in the Black Sea region".
Russia had fired warning shots last week at the HMS Defender after what it said was a violation of its territorial waters.
Russia annexed Crimea from Ukraine in 2014 and claims the waters around the peninsula as part of its territory. Most countries do not recognise the takeover and stand behind Ukraine's claims to the waters.
Russia conducts live-fire training exercise in the Black Sea
Russian warships carried out a live-fire training exercise in the Black Sea, the country's Black Sea fleet said as Ukraine and NATO countries held military drills in the same wider area.
The Sea Breeze drills, led by Ukraine and the United States, follow a spike in tensions between NATO and Moscow after Russia last week said it had fired warning shots and dropped bombs in the path of a British warship to expel it from its territorial waters near Crimea.
London said it did not recognise Moscow's account of the incident near the peninsula, which Russia annexed from Ukraine in 2014.
Russia's Black Sea fleet
Moscow had called for the Sea Breeze exercise to be cancelled before it began, and the Russian defence ministry has said it will react to safeguard national security if necessary.
Russia's Black Sea fleet said in a statement on Thursday carried by the Interfax news agency that the crews of two large landing ships had fired at sea and air targets in the Black Sea.
The drill came two days after Russia tested its air defence systems in Crimea.
US deploys destroyer USS Ross and Marine Corps
In separate comments, Russia's defence ministry said it was tracking an Italian navy frigate after it entered the Black Sea on Thursday, Interfax reported.
Sea Breeze 2021 will last two weeks and involve about 5,000 military personnel from NATO and other allies, and around 30 ships and 40 aircraft, with US missile destroyer USS Ross and the US Marine Corps taking part.
MI-8 helicopters, SU-25 and SU-27
The US-led Operation Sea Breeze drills involve MI-14 and MI-8 helicopters, SU-25 and SU-27 which were focused on practising parachuting skills among others.
Ukraine says the main goal is to gain experience in joint actions during multinational peacekeeping and security operations.
Sea Breeze 2021 follows a rise in tensions between NATO and Moscow, which said last week it had fired warning shots and dropped bombs in the path of a British warship to chase it out of Black Sea waters off the coast of Crimea. Britain rejected Russia's account of the incident.
Tensions simmer in the Black Sea
As tensions simmered in the Black Sea, the Russian Air Force and the navy carried out joint drills in the Mediterranian Sea, and trained in preventing air attacks.
The country's defence ministry on June 28 in a video showed its jets flying over the military vessels. The exercises included five ships and two submarines, according to the ministry.
Russia's Defence Ministry began a joint Navy and Air Force exercises in the eastern Mediterranean, where Moscow operates an airbase on Syria's coast.
Hmeymin airbase was built in 2015 when Russia intervened militarily in the Syrian conflict.