NATO commander General Philip Breedlove warned that Russia's annexation of Crimea could give the country total control over the Black Sea, according to The Cable.
The general made the statement on Wednesday while in Kiev, Ukraine, to address the country's leaders.
After Russia took over Crimea in March of this year, it has increased its military presence in the peninsula with the deployment of ground troops and aircrafts.
General Breedlove said by militarizing Crimea, Russia could gain exclusive access to the Black Sea and gain significant strategic advantage.
"We are very concerned with the militarization of Crimea," he said during a press conference. "We are concerned that the capabilities in the Crimea that are being installed will bring an effect on almost the entire Black Sea."
"This international border is completely wide open and maintained open by Russian forces, so that forces, supplies, money, fighters can move across at will," the general added.
Aside from Russia's operations in Crimea, NATO is also monitoring the country's newly formed ties with Adkhazia, a separatist and independent state in Georgia that also borders the Black Sea, Business Insider reported.
As part of the treaty signed by President Vladimir Putin and Abkhazia's President Raul Khadzhimba, the military force of the latter will be controlled by a Russian commander.
NATO criticized the treaty and said it goes against Georgia's sovereignty since Abkhazia is part of its territory.
"This so-called treaty does not contribute to a peaceful and lasting settlement of the situation in Georgia," Secretary General Jens Stoltenberg said in a statement.
"On the contrary, it violates Georgia's sovereignty and territorial integrity and blatantly contradicts the principles of international law, OSCE principles and Russia's International commitments," Stoltenberg added.
Like the international alliance, the U.S. State Department said in a press release that it is against the agreement between Russia and Abkhazia.
"The United States will not recognize the legitimacy of any so-called 'treaty' between Georgia's Abkhazia region and the Russian Federation," the government agency stated.
