From Wikipedia: Law enforcement agency: In North American English, a law enforcement agency (LEA) is an government agency responsible for the enforcement of the laws. Outside North America, such organizations are called police services.
Notice that all police agencies are law enforcement agencies, but all law enforcement agencies are not police agencies. For example, the United States Coast Guard may be considered a law enforcement agency, but is is not a police agency -- it is instead a military service. In the same way, the Criminal Investigation Division of the Internal Revenue Service is also a law enforcement agency (it investigates tax fraud and violations of the tax laws), but it is not usually thought of as a police agency.