security force; public safety force
Refers to an organized group, often official or military, tasked with maintaining public order and safety.
The government dispatched security forces to quell the riot.
The public safety force protects the safety of the city.
警察 refers specifically to the police as a civil law enforcement agency, while 治安部隊 is a broader term that can include military or paramilitary units focused on public order.
自衛隊 is Japan's Self-Defense Forces, a military organization for national defense; 治安部隊 is a more general term for any force maintaining public safety, not limited to Japan.
Compound of 治安 (public peace, security) and 部隊 (unit, corps). The word is a straightforward modern formation from Sino-Japanese elements.