Video has surfaced that appears to show tanks being maneuvered into position by Russian soldiers along the Ukrainian border.
As The New York Post reports, the clips show a number of armoured vehicles congregating in a muddy field, followed by a train carrying military-style trucks, then a crane-like machine behind a fence.
Tensions have been heightened in the region ever since Russia annexed the Crimea region of Ukraine in 2014. The move led to US and EU sanctions being placed on Russia.
The Navy is reportedly "flying reconnaissance aircraft in international airspace over the Black Sea to monitor Russian naval movements".
According to The New York Post, the Biden administration has stated that American warships may be sent to the Black Sea in the coming weeks in response to Russia's aggression. The United States must give 14 days notice if it plans to move ships into the area, according to a 1936 Treaty that gave Turkey control over the surrounding straits.
American officials have been in contact with their Ukrainian counterparts, and are monitoring the situation closely.