Aggressive tactics from Russian forces on the border with Ukraine and other activity have prompted widespread condemnation from the West, while the Kremlin has brushed off accusations.
The size and power of the Russian armed forces secure its position as a global power, while the US maintains that its place in military alliances adds to its strength.
Here's how the two militaries stack up in numbers and equipment, according to the 'Military Balance 2021' report from the International Institute for Strategic Studies (IISS).
This comparison gives a snapshot of how the two forces compare in conventional domains, using the latest reliable data in 2021.
Defence Budget (2020) [US dollars] – Russia: $60.6bn, US: $738bn
Active Personnel – Russia: 900,000, US: 1,388,100
Reserve Personnel – Russia:2,000,000, US: 844,950
Intercontinental Ballistic Missile (ICBM) Launchers – Russia: 336, US: 400.
Bomber Aircraft - Russia: 137, US: 157
Fighter And Ground Attack Aircraft – Russia: 1,021, US: 3,318
Attack Helicopters – Russia: 402, US: 867
Heavy Unmanned Aerial Vehicles – Russia: Some (under 50), US: 625
Heavy/Medium Transport Helicopters and Tilt-Rotor Aircraft – Russia: 368, US: 3,033
Heavy/Medium Transport Aircraft – Russia: 190, US: 686
Tanker and Multi-Role Tanker/Transport Aircraft – Russia: 15, US: 567
Airborne Early-Warning And Control Aircraft – Russia: 9, US: 125
Watch: U-2: All About America's Secret Spy Plane.
Armoured Infantry Fighting Vehicles – Russia: 6,450, US: 3,419
Main Battle Tanks - Russia: 3,330, US: 2,509
Artillery – Russia: 5,689, US: 6,941
Ballistic-Missile Nuclear-Powered Submarines – Russia: 11, US: 14
Attack/Guided Missile Submarines – Russia: 38, US: 54
Aircraft Carriers - Russia: 1, US: 11
Cruisers, Destroyers and Frigates - Russia: 30, US: 113
Principal Amphibious Ships – Russia: 5, US: 32
The United States Special Operations Command (USSOCOM) oversees global special operations and activities, bringing together a network of elite commands from the US Army, navy, marine corps and air force.
Reconnaissance, hostage rescue and recovery, countering weapons of mass destruction and counterterrorism are all part of the USSOCOM mission.
63,150 personnel and 6,550 civilians fall under USSOCOM.
Russia's Special Operations Forces are 1,000-strong, while the country has special forces units in its air, naval infantry (marines) and airborne forces.
Spetsnaz, Russian special military operators, are present in each of the five Russian military districts – the defence structure dividing military jurisdiction across the country's huge land mass.
Cyber and Space
The US Cyber Command is commanded by the National Security Agency and contains 133 Cyber Mission Teams, maintaining the ability to ability to conduct cyber attacks across all warfighting domains, as part of a 'defend-forward' strategy.
This is similar to the front-foot approach taken by the National Cyber Force in the UK.
Russia considers cyber a space to be protected by its armed forces, though its command chain in the domain is often blurred with civilian bodies.
The US authorities consider Russia's Directorate of the General Staff (GRU) and certain subordinate units principle actors in offensive cyber and influence operations, according to the IISS.
In space, the US Space Force continues to establish itself in the newly-declared warfighting domain, with more than 2,000 personnel drawn from around the military.
Protecting allied satellites and providing greater intelligence for operations on Earth remains the focus of the branch.
The US and Russia both possess Intelligence, Surveillance, Reconnaissance equipment, while Russian Space Command leases radar technology from neighbouring states.
Both have communications and satellite equipment, although the US also possesses counter communications systems in space.
Cover image: A Russian tank on exercise in 2019 (Picture: Russian MOD).