By Nate Raymond

NEW YORK (Reuters) - Two former Chinese diplomats working at a construction company face U.S. charges that they schemed to force employees who received visas to perform work only at China's U.N. mission and other facilities to instead provide private contracting work.

A criminal complaint against Dan Zhong and Landong Wang made public on Tuesday in Brooklyn federal court said the sites that received private contracting work included a Long Island residence matching the description of one tied to a U.N. bribery case.

That $10-million mansion was owned by a Chinese associate of Ng Lap Seng, a Macau billionaire accused of bribing a U.N. diplomat who was questioned by the FBI about the homeowner's intelligence ties, according to court records.

Zhong, 46, was ordered held without bail at a court hearing on Saturday. It was unclear whether Landong Wang was in custody.

A spokeswoman for the U.S. Attorney's office in Brooklyn declined comment. Zhong's lawyer did not respond to requests for comment.

The complaint said Zhong was the principal of a Chinese construction company's U.S. operations, while Wang was a manager. Both were former diplomats of China, it said.

The complaint said their company hired Chinese workers who received visas solely to perform construction work at China's U.N. mission or other diplomatic facilities.

Instead, they were forced by physical restraint, threats and abuse to perform contracting work at private sites, the complaint said, including the Long Island residence and a home owned by a Chinese-born airline worker.

In Beijing, Foreign Ministry spokesman Geng Shuang told reporters the two men were employees of a construction firm sent to work in the United States.

Building projects for China's U.N. mission and other bodies in the United States respect pacts between the two countries, and China has always protected the rights and safety of citizens overseas, Geng added.

Prosecutors did not name the airline employee or the owner of the Long Island residence.

But their descriptions matched those of Ying Lin, an ex-Air China Ltd employee, and Qin Fei, who, Ng has said, was a consultant to his real estate company.

FBI agents last year interrogated Ng about Qin, asking if he was connected to foreign intelligence, court records show.

Prosecutors have accused Lin of assisting military personnel at China's U.N. mission to smuggle packages out of the United States and helping Qin flee to China amid an FBI investigation.

Lin has pleaded not guilty. Her lawyer did not respond to requests for comment. Qin, who has not been charged, did not respond to requests for comment.

Ng is set to face trial in January on charges that he bribed a former U.N. General Assembly president to support a Macau-based conference center his company would develop. He has pleaded not guilty.

(Additional reporting by Ben Blanchard in Beijing; Editing by G Crosse and Clarence Fernandez)