Russia will restrict the navigation of foreign military and official ships in parts of the Black Sea until October, a Russian news agency reported Friday, a move that was swiftly condemned by Ukraine and the EU.
Tensions between Moscow and Kiev have escalated in recent weeks following an uptick in fighting between Ukraine's army and pro-Russia separatists in eastern Ukraine.
Russia has massed its troops along Ukraine's northern and eastern borders and on the Crimean peninsula, which Moscow annexed from Ukraine in 2014. This week Russia also conducted navy drills in the Black Sea.
"From 21:00 on April 24 until 21:00 on Oct. 31, passage through the territorial sea of the Russian Federation for foreign military ships and other state vessels will be halted," the state-run RIA Novosti news agency cited a Defense Ministry statement as saying.
The restrictions will affect the western tip of Crimea, the peninsula's southern coastline from Sevastopol to Hurzuf, and a "rectangle" off the Kerch peninsula near the Opuksky Nature Reserve.
A senior European Union official described the move as a "highly worrying development."
The move contradicts norms of free maritime passage and international law and adds to tensions around "the military buildup on the other side of the Russian border with Ukraine," the official told AFP.
The official added that the restrictions would increase tensions as Russia was "taking unilateral measures on an international space."
One of the areas affected by Russia's restrictions is located near the Kerch Strait, which connects the Black Sea to the Sea of Azov and is of crucial importance for the export of grain and steel from Ukraine.
The Kerch Strait became a scene of confrontation in 2018 after Russia seized three Ukrainian ships there over alleged violations of its territorial waters.
Ukraine had been free to navigate the Kerch Strait along with Russia until 2014, when Moscow claimed full control of the waterway after annexing Crimea.
The Kerch Strait is also the site of a costly 19-kilometer (12-mile) bridge connecting Crimea with mainland Russia that Moscow opened in 2018.
Ukraine's foreign ministry on Thursday slammed the navigation restrictions, which were initially reported without specifics earlier this week, as a "usurpation of the sovereign rights of Ukraine."
It also stressed that under the UN Convention on the Law of the Sea, "Russia must neither obstruct or halt transit through the international strait to ports in the Sea of Azov."