U.S. Customs and Border Protection (CBP) is the primary enforcement arm of the United States for immigration laws, where it makes arrests at Ports-of-Entry (POE) and within the United States, primarily near the land or maritime borders of the United States, though their authority to make arrests includes all of the United States.
The components of CBP that primarily make arrests of aliens for immigration law violations are the United States Border Patrol (USBP), which operates outside the POEs, and the Office of Field Operations (OFO), which operates at POEs, where it examines arriving American citizens and/or nationals and inspects arriving aliens.
The purpose of the USBP enforcement activities is to prevent illegal entry by aliens through the borders of the United States or arrest those who were not prevented from entering, while the OFO’s enforcement activities are to prevent the admission of aliens ineligible for admission at POEs.