The Marine Corps Embassy Security Group, formerly Marine Security Guard Battalion, and also known as Marine Security Guards or Marine Embassy Guards, are members of the Marine Corps Embassy Security Group, a battalion

Battalion

A battalion is a military unit of around 300–1,200 soldiers usually consisting of between two and seven companies and typically commanded by either a Lieutenant Colonel or a Colonel...

-sized organization of U.S. Marines

United States Marine Corps

The United States Marine Corps is a branch of the United States Armed Forces responsible for providing power projection from the sea, using the mobility of the United States Navy to deliver combined-arms task forces rapidly. It is one of seven uniformed services of the United States...

 that have detachments posted at American Embassies, American Consulates and other official United States Government offices such as the U.S. Interests Section

United States Interests Section in Havana

The U.S. Naval Base at Guantanamo Bay is inaccessible from within Cuba. Consular issues regarding the naval base are handled by the U.S. Embassy in Kingston, Jamaica.-Location:...

, located in Havana

Havana

Havana is the capital city, province, major port, and leading commercial centre of Cuba. The city proper has a population of 2.1 million inhabitants, and it spans a total of — making it the largest city in the Caribbean region, and the most populous...

, Cuba

Cuba

The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...

, or the United States Mission to NATO located in Brussels, Belgium.
The Marine Corps has a long history of cooperation with the Department of State, going back to the early days of the nation.