An FBI agent may have accidentally killed a Puerto Rican policeman in a late-night shootout with alleged kidnappers, the island's top police official said Friday.

Police Superintendent Pedro Toledo said evidence collected so far suggests the 12-year veteran, who was in uniform, was struck by stray bullets during an FBI raid to rescue a kidnap victim from the Dominican Republic.

"According to the witnesses we have interviewed, there is a significant possibility that he died from what we call 'friendly fire,' shots from the gun of an FBI agent," Toledo said.

The FBI planned to dispatch a team of investigators from the U.S. mainland to investigate the incident, said spokesman Harry Rodriguez.

The agency is testing weapons from the agents at the scene to determine if one of them fired any of the shots that struck the officer, said Luis Fraticelli, head of the FBI in the U.S. island territory.

Agents and officers descended on the quiet neighborhood east of San Juan around midnight. Toledo said the kidnappers had the victim in the trunk of a car and were demanding US$650,000.

As FBI agents freed the man, the kidnappers fled in an SUV then crashed into another vehicle. Toledo said a second group of U.S. agents fired at the kidnappers, and the officer, who was guarding a side street, was hit by stray bullets that penetrated through gaps in his body armor.

Three suspects were caught, but two escaped, officials said.