Romania has reportedly started construction on a huge expansion of a military base near the Black Sea that will be the largest used by the NATO alliance, and it sits within 300 miles of land occupied by Russian forces. 

The Mihail Kogalniceanu Romanian Air Force is located in Constanta, Romania which sits 275 miles across the Black Sea from Crimea.

When fully constructed, the €2.5 billion ($2.7 billion) base will reportedly be the size of a small city and house 10,000 NATO troops and their families, according to Euronews.

The massive project includes building runways, hangers, housing, a hospital and schools.

In July 2015, the NATO Investment Committee approved a significant renovation plan for the base.

The investment will be implemented in four stages over 20 years and include various works such as terrain arrangement works, runway and taxiway construction..

The new flight line will provide a flight traffic control post, aircraft operating platforms, lighting and radar systems.

The project also includes administrative and social facilities, transit and storage areas, aircraft maintenance areas, military equipment warehouses, perimeter fence and access post control, according to NATO.

The base currently hosts 5,000 NATO soldiers, mainly American but there are no families currently housed at the base.

Planes from several NATO members are cycled through the base to help secure the airspace over the Black Sea region. 

The U.S. also used the base to support operations when combat troops were in Afghanistan.

Moscow has consistently warned the US and its allies against NATO's eastward expansion and military buildup near Russia's borders.

Russian President Vladimir Putin has issued a direct warning of nuclear retaliation against the West, alleging that NATO and the US are planning to attack Russia.

The 71-year-old Russian president has emphasized the formidable capabilities of Russia's weaponry and underscored the risk of a conflict involving nuclear weapons, posing a serious threat to global civilization.