PROVIDENCE, R.I. – The top federal prosecutor in Rhode Island warned Gov. Lincoln Chafee on Friday that the state’s plan to license medical marijuana dispensaries appears to violate federal law.

U.S. Attorney Peter F. Neronha said in a letter hand-delivered to Chafee’s office that federal prosecutors could investigate and prosecute dispensaries that grow and distribute marijuana, even if the dispensaries are acting under state oversight.

“The Department of Justice maintains the authority to enforce (federal drug laws) vigorously against individuals and organizations that participate in unlawful manufacturing and distribution activity involving marijuana, even if such activities are permitted under state law,” Neronha wrote Chafee in the three-page letter.

A spokesman for Chafee said the letter is under review. Chafee, an independent, was in Baltimore on Friday on an economic development research trip.

The Department of Justice does not target “seriously ill” individuals using marijuana in accordance with state medical marijuana laws, Neronha wrote. But prosecutors could pursue civil and criminal penalties for dispensaries, he wrote, because the state’s rules “appear to permit large-scale marijuana cultivation and distribution.”

The state announced last month that it had picked three organizations to serve as state-regulated dispensaries for medical marijuana. The so-called “compassion centers” are the Greenleaf Compassionate Care Center of Portsmouth, Summit Medical Compassion Center of Warwick and the Thomas C. Slater Compassion Center of Providence.

Before opening, the dispensaries must pass a state inspection and receive local occupancy permits, and employees must pass criminal background checks. The permitting process is expected to take months. Qualified patients will then be allowed to designate one of the centers as their authorized source of marijuana.

Fifteen states, including Maine, have legalized marijuana for medical purposes. Federal prosecutors have recently delivered similar warnings about medical marijuana dispensaries in Colorado and Washington.

Rhode Island state Sen. Rhoda Perry, a Providence Democrat who worked closely on the dispensary legislation, said many lawmakers thought that President Obama’s administration would not target marijuana dispensers that follow state law. She’s not sure what to make of Neronha’s letter.

“I’m bamboozled,” Perry said. “I’m very disturbed. We have a very reasoned approach. It’s a complete reversal.”

Rhode Island enacted a law in 2006 allowing patients to legally possess small amounts of marijuana to treat conditions including chronic pain, severe nausea, seizures and multiple sclerosis. In 2009, lawmakers passed legislation to set up nonprofit compassion centers where patients could obtain marijuana in a state-regulated environment.

Operators of Rhode Island’s three compassion centers could not be reached for comment late Friday.Fifteen states, including Maine, have legalized marijuana for medical purposes. Federal prosecutors have recently delivered similar warnings about medical marijuana dispensaries in Colorado and Washington.