ABU DHABI, United Arab Emirates - Late one night last November, a plane carrying dozens of Colombian men touched down in this glittering seaside capital. Whisked through customs by an Emirati intelligence officer, the group boarded an unmarked bus and drove roughly 20 miles to a windswept military complex in the desert sand.

The Colombians had entered the United Arab Emirates posing as construction workers. In fact, they were soldiers for a secret American-led mercenary army being built by Erik Prince, the billionaire founder of Blackwater Worldwide, with $529 million from the oil-soaked sheikdom.

Mr. Prince, who resettled here last year after his security business faced mounting legal problems in the United States, was hired by the crown prince of Abu Dhabi to put together an 800-member battalion of foreign troops for the U.A.E., according to former employees on the project, American officials and corporate documents obtained by The New York Times.

The force is intended to conduct special operations missions inside and outside the country, defend oil pipelines and skyscrapers from terrorist attacks and put down internal revolts, the documents show. Such troops could be deployed if the Emirates faced unrest or were challenged by pro-democracy demonstrations in its crowded labor camps […]