WASHINGTON — The United Arab Emirates has secretly dispatched hundreds of Colombian mercenaries to Yemen to fight in that country’s raging conflict, adding a volatile new element in a complex proxy war that has drawn in the United States and Iran.

It is the first combat deployment for a foreign army that the Emirates has quietly built in the desert over the past five years, according to several people currently or formerly involved with the project. The program was once managed by a private company connected to Erik Prince, the founder of Blackwater Worldwide, but the people involved in the effort said that his role ended several years ago and that it has since been run by the Emirati military.

The arrival in Yemen of 450 Latin American troops — among them are also Panamanian, Salvadoran and Chilean soldiers — adds to the chaotic stew of government armies, armed tribes, terrorist networks and Yemeni militias currently at war in the country. Earlier this year, a coalition of countries led by Saudi Arabia, including the United States, began a military campaign in Yemen against Houthi rebels who have pushed the Yemeni government out of the capital, Sana.

It is also a glimpse into the future of war. Wealthy Arab nations, particularly Saudi Arabia, Qatar and the Emirates, have in recent years embraced a more aggressive military strategy throughout the Middle East, trying to rein in the chaos unleashed by the Arab revolutions that began in late 2010. But these countries wade into the new conflicts — whether in Yemen, Syria or Libya — with militaries that are unused to sustained warfare and populations with generally little interest in military service.