Several employees of American Airlines were among a group of at least 20 people arrested Tuesday on suspicion of aiding a smuggling ring that shipped drugs from Puerto Rico's main airport to the U.S. mainland.

U.S. federal agents and Puerto Rican police swarmed the Luis Munoz Marin International Airport in San Juan to make the arrests, said a law enforcement official who spoke on condition of anonymity because he was not authorized to reveal details of the investigation.

Several ground crew employees of American Airlines are suspected of helping to transport drugs from South America and the Caribbean to the United States, the official said. He said 23 arrest warrants have been issued in cities across the U.S. Caribbean territory and Miami.

American spokeswoman Minnette Velez confirmed the arrest of airline employees but gave no details.

"We work with the authorities whenever we identify a situation like this, which is unacceptable," Velez told The Associated Press. "We work to make sure this doesn't happen."

As a U.S. territory, Puerto Rico is a favored transshipment point for South American cocaine and heroin because once the drugs reach the Caribbean island, they do not have to pass through customs on the way to the American market.