Five U.S Army soldiers are under investigation for allegedly trying to smuggle 32 pounds of cocaine out of Colombia (search) aboard a U.S. military aircraft, American officials said Thursday.

The soldiers were detained Tuesday as a result of the investigation, said Lt. Col. Eduardo Villavicencio, a spokesman for the U.S. military's Southern Command in Florida.

He would not disclose where the five are being held, other than "in the United States."

"The Department of Defense is working closely with Colombian authorities and U.S. law enforcement to conduct a thorough investigation," William Wood, the U.S. ambassador to Colombia, said in a statement. "I congratulate our law enforcement agencies for their excellent cooperation in uncovering this drug smuggling scheme." The embassy declined further comment.

Colombia's Defense Ministry confirmed an investigation was underway, but wouldn't discuss details of the case.

The United States has provided more than $3 billion in aid over the past four years to help Colombia battle Marxist rebels and drug trafficking that fuels the 40-year-old insurgency.

Up to 800 U.S. troops are permitted in Colombia, according to U.S. law, to train Colombian armed forces and to provide logistical support. Up to 600 Americans are also permitted in the country as U.S. government contractors.

It was the second major scandal to hit the U.S. military in Colombia.

In 1999, the wife of the former commander of U.S. anti-drug operations in Colombia, Laurie Hiett, pleaded guilty to shipping $700,000 in cocaine and heroin to New York City in diplomatic parcels. She was sentenced to five years in prison.

Her husband, Col. James C. Hiett, pleaded guilty to helping his wife launder $25,000 in illicit profits and was given a five-month prison term.

The case embarrassed the Pentagon at a time when former President Clinton was pitching the billion-dollar plan to back Colombian forces. Colombia is the world's largest producer of cocaine and a major supplier of heroin to the United States.