The FBI on Tuesday arrested 10 Puerto Rico police officers accused of stealing drugs and cash, planting evidence and taking bribes, prompting the U.S. territory's police chief to pledge a widespread restructuring of his department as it struggles to crack down on corruption.

The suspects, members of the police anti-drug units, include a lieutenant and a sergeant. FBI officials said they expect further arrests in the case, part of an ongoing series of probes into the troubled department.

"These officers used their badges and abused their authority," said U.S. Attorney Rosa Emilia Rodriguez. "What appeared to be a legitimate police operation was nothing else but an organized criminal act."

Federal prosecutors said the suspects, working out of the main police precinct, divvied up some $175,000 in proceeds generated from stealing drugs and cash during legal and illegal raids.

In one instance, authorities said some of the suspects released a federal drug-trafficking fugitive in exchange for two high-powered rifles.

Prosecutors also said they are investigating whether some people arrested by the accused officers are currently in jail as a result of false testimony or planted evidence.

Police Chief Jose Caldero said he will restructure the department's 16 anti-narcotics units and require those in them to undergo polygraph tests, a first for the island's police agency. There are currently 320 officers in those divisions.

"We will clean house," he vowed. "We will not tolerate corruption."

Puerto Rico's police department is the second largest in a U.S. jurisdiction, and more than 100 officers have been arrested in the past five years on corruption charges.

In 2010, the FBI arrested 89 law enforcement officers across Puerto Rico in what it said was the largest police corruption investigation in the agency's history.

A year later, U.S. prosecutors issued a scathing report that accused Puerto Rico police officers of illegal killings, corruption and civil rights violations. As a result, the island's police department is undergoing a 10-year federally mandated reform.

Authorities say they have hired consultants, trained officers on the use of force, established a reform office and appointed a monitor as part of the changes.

Critics say the reform process has been slow and incomplete, and police officials have acknowledged that they have struggled to resolve a large backlog of civilian complaints.

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Danica Coto on Twitter: www.twitter.com/danicacoto