A four-week military exercise by US land, sea and air forces in Europe have raised the alarm bells in Russia which sees the drill as "an unprecedentedly dangerous step" at its front door.
The United States scaled up the Operation Atlantic Resolve staged from Estonia in the north to Bulgaria in the south since last year to reassure NATO allies of US support in the face of Russian “aggression” in Ukraine.
The destroyer Jason Dunham entered the Black Sea on April 3 to join a number of other ships participating in the NATO drills.
The US Army also deployed 750 tanks and thousands of troops to Lithuania, Latvia and Estonia "to deter Russian aggression."
US Army Europe said in a statement last month that the forces will remain deployed for about nine months.
A Russian Foreign Ministry spokesman denounced the maneuvers as "an unprecedentedly dangerous step."
"It takes F-16 fighters just a few minutes to reach St. Petersburg," Alexander Lukashevich said, referring to the major Russian port city on the Baltic Sea.
Experts say the large-scale war games have essentially put US and Russian forces back in a Cold War-style standoff, warning that a misinterpretation of a move by either side could trigger a major conflict.
"A dangerous game of military brinkmanship is now being played in Europe," Ian Kearns, director of the European Leadership Network, told the Associated Press.
"If one commander or one pilot makes a mistake or a bad decision in this situation, we may have casualties and a high-stakes cycle of escalation that is difficult to stop," he added.
Earlier this week, the commander of the US Northern Command also warned about Russia’s growing military moves near US borders.
"They're messaging us that they're a global power," Adm. William Gortney told reporters during a Pentagon briefing on Tuesday. "We watch very carefully what they're doing."