Ukraine on Thursday "strongly protested" a decision by Russia to block parts of the Black Sea, Sea of Azov and Kerch Strait "under the pretext of holding regular naval exercises."
"Unprecedented coverage of maneuvers makes navigation in both seas virtually impossible. In essence, this is a significant and unjustified complication of international shipping, especially trade, which can cause complex economic and social consequences, especially for the ports of Ukraine," the country's Foreign Ministry said in a statement.
The ministry deemed unacceptable such "aggressive actions" by Moscow, which it said "fit into the concept of its hybrid war against Ukraine."
The Sea of Azov lies northeast of the Crimean Peninsula, which Russia annexed from Ukraine in March 2014. It is connected to the Black Sea by the narrow Kerch Strait.
Russia's annexation of Crimea has been labeled illegal by the EU, Turkiye, and the UN General Assembly.
"This is a manifestation of open disregard for the norms and principles of international law, including the UN Charter, UN General Assembly resolutions and the UN Convention on the Law of the Sea," it added.
The statement emphasized that Ukraine is "closely working" with partners, primarily those in the Black Sea region, to ensure that such Russian actions "receive a proper assessment and response."
Recently, Russia amassed thousands of troops near Ukraine's borders, prompting fears it could be planning another military offensive against the former Soviet republic.
The US and its allies have warned of an imminent attack, and threatened Russia with "severe consequences."
Moscow, however, has denied it is preparing to invade Ukraine and said its troops are there for exercises.