SAN JUAN, Puerto Rico—Federal authorities in Puerto Rico say they have seized 320 pounds (145 kilograms) of cocaine and arrested six people from the Dominican Republic on suspicion of trafficking drugs.

The Immigration and Customs Enforcement agency says in a statement that authorities seized the drugs several miles north of Puerto Rico after a customs plane detected a ship traveling toward the U.S. Caribbean territory early Friday.

The agency said federal agents and Puerto Rico police also seized 18 pounds (eight kilograms) of heroin.