By EMILY B. HAGER and MARK MAZZETTI

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.

“Mercenaries are an attractive option for rich countries who wish to wage war yet whose citizens may not want to fight,” said Sean McFate, a senior fellow at the Atlantic Council and author of “The Modern Mercenary.”

“The private military industry is global now,” said Mr. McFate, adding that the United States essentially “legitimized” the industry with its heavy reliance on contractors in Iraq and Afghanistan over more than a decade of war. “Latin American mercenaries are a sign of what’s to come,” he said.

The Colombian troops now in Yemen, handpicked from a brigade of some 1,800 Latin American soldiers training at an Emirati military base, were woken up in the middle of the night for their deployment to Yemen last month. They were ushered out of their barracks as their bunkmates continued sleeping, and were later issued dog tags and ranks in the Emirati military. Those left behind are now being trained to use grenade launchers and armored vehicles that Emirati troops are currently using in Yemen.

Emirati officials have made a point of recruiting Colombian troops over other Latin American soldiers because they consider the Colombians more battle tested in guerrilla warfare, having spent decades battling gunmen of the Revolutionary Armed Forces of Colombia, or FARC, in the jungles of Colombia.

The exact mission of the Colombians in Yemen is unclear, and one person involved in the project said it could be weeks before they saw regular combat. They join hundreds of Sudanese soldiers whom Saudi Arabia has recruited to fight there as part of the coalition.

In addition, a recent United Nations report cited claims that some 400 Eritrean troops might be embedded with the Emirati soldiers in Yemen — something that, if true, could violate a United Nations resolution restricting Eritrean military activities.

The United States has also been participating in the Saudi-led campaign in Yemen, providing logistical support, including airborne refueling, to the nations conducting the airstrikes. The Pentagon has sent a team to Saudi Arabia to provide targeting intelligence to the coalition militaries that is regularly used for the airstrikes.

The Obama administration has also in recent years approved the sale of billions of dollars’ worth of military hardware from American contractors to the Saudi and Emirati militaries, equipment that is being used in the Yemen conflict. This month, the administration authorized a $1.29 billion Saudi request for thousands of bombs to replenish stocks that had been depleted by the campaign in Yemen, although American officials say that the bombs would take months to arrive and were not directly tied to the war in Yemen.

The Saudi air campaign has received widespread criticism from human rights groups as being poorly planned and as having launched strikes that indiscriminately kill Yemeni civilians and aid workers in the country. Last month, Saudi jets struck a hospital run by Doctors Without Borders in Saada Province in northern Yemen, and in late September the United Nations reported that 2,355 civilians had been killed since the campaign began in March.

On the other side in Yemen is Iran, which over the years has provided financial and military support to the Houthis, the Shiite rebel group fighting the coalition of Saudi-led Sunni nations. The divisions have created the veneer of a sectarian conflict, although Emirati troops in southern Yemen have also been battling members of Al Qaeda in the Arabian Peninsula, the Sunni terrorist group’s affiliate in Yemen.

Dozens of Emirati special operations troops have died since they arrived in southern Yemen in August. A single rocket attack in early September killed 45, along with several Saudi and Bahrani soldiers.

The presence of the Latin American troops is an official secret in the Emirates, and the government has made no public mention of their deployment to Yemen. Yousef Otaiba, the Emirati ambassador to Washington, declined to comment. A spokesman for United States Central Command, the military headquarters overseeing America’s involvement in the Yemen conflict, also declined to comment.

The Latin American force in the Emirates was originally conceived to carry out mostly domestic missions — guarding pipelines and other sensitive infrastructure and possibly putting down riots in the sprawling camps housing foreign workers in the Emirates — according to corporate documents, American officials and several people involved in the project.

A 2011 intelligence briefing for senior leaders involved in the project listed Al Qaeda in the Arabian Peninsula, Somali pirates and domestic riots as some of the biggest threats to Emirati stability.

The troops were told that they might one day be called for foreign combat missions, but until the deployment to Yemen the only external missions they were given were to provide security on commercial cargo vessels.

Those missions were rare, and soldiers involved in the project describe years of monotony at the desert camp, housed within a sprawling Emirati military base called Zayed Military City. They rise every day at 5 a.m. for exercise and military training — including shooting practice, navigation and riot control. A number of Westerners, including several Americans, live at the camp and serve as trainers for the Latin American troops.

But by late morning the sun burns so hot at the windswept complex that the troops move into air-conditioned classrooms for military instruction.

The troops live in typically austere military barracks, hanging their laundry out the windows to dry in the hot air. There is a common computer room where they can check their email and Facebook pages, but they are not allowed to post photographs on social media sites. Meals are basic.

“It’s the same food all the time, every day,” one member of the project said several weeks ago. “Chicken every single day.”

The Emiratis have spent the equivalent of millions of dollars equipping the unit, from firearms and armored vehicles to communications systems and night vision technology. But Emirati leaders rarely visit the camp. When they do, the troops put on tactical demonstrations, including rappelling from helicopters and driving armored dune buggies.

And yet they stay largely because of the money, receiving salaries ranging from $2,000 to $3,000 a month, compared with approximately $400 a month they would make in Colombia. Those troops who deploy to Yemen will receive an additional $1,000 per week, according to a person involved in the project and a former senior Colombian military officer.

Hundreds of Colombian troops have been trained in the Emirates since the project began in 2010 — so many that the Colombian government once tried to broker an agreement with Emirati officials to stanch the flow headed to the Persian Gulf. Representatives from the two governments met, but an agreement was never signed.

Most of the recruiting of former troops in Colombia is done by Global Enterprises, a Colombian company run by a former special operations commander named Oscar Garcia Batte. Mr. Batte is also co-commander of the brigade of Colombian troops in the Emirates, and is part of the force now deployed in Yemen.

Mr. McFate said that the steady migration of Latin American troops to the Persian Gulf had created a “gun drain” at a time when Latin American countries need soldiers in the battle against drug cartels.

But experts in Colombia said that the promise of making more money fighting for the Emirates — money that the troops send much of home to their families in Colombia — makes it hard to keep soldiers at home.

“These great offers, with good salaries and insurance, got the attention of our best soldiers,” said Jaime Ruiz, the president of Colombia’s Association of Retired Armed Forces Officials.

“Many of them retired from the army and left.”