SAN JUAN, Puerto Rico –  Two bystanders were killed during a shootout Thursday after gunmen robbed an armored car outside a bank in western Puerto Rico, police said.

Police spokesman Jonathan Matias said two bank customers were killed when they were caught in the exchange of gunfire between the robbers and security guards. He said one security guard was wounded by several bullets and investigators believed one of the robbers might have been wounded.

The guard, identified as Anibal Acevedo, was taken to Puerto Rico's largest hospital, in the capital of San Juan. His condition was unknown late in the day, the security company Ranger American said.

Matias said police were not sure how many gunmen were involved in the robbery in the coastal town of Anasco. The robbers fled in a stolen car and made off with an undetermined amount of money, he said. The car was found several hours later, but the suspects were still on the run, police said.

FBI spokesman Carlos Osorio said the agency was taking over the case, but he did not have additional details.

The dead bystanders were identified as Ariel Nunez, 49, and Waldemar Mendez, 36, both from the nearby town of Aguada. Mendez worked as a government prison guard.

The U.S. territory of 3.4 million people reported 679 killings last year, a 16 percent increase from the previous year.