WASHINGTON — The Pentagon will begin deploying as many as 1,500 active duty troops to help secure the southern border in the coming days, U.S. officials said Wednesday, putting in motion plans President Donald Trump laid out in executive orders shortly after he took office to crack down on immigration.

Acting Defense Secretary Robert Salesses was expected to sign the deployment orders on Wednesday, but it wasn’t yet clear which troops or units will go, and the total could fluctuate. It remains to be seen if they will end up doing law enforcement, which would put American troops in a dramatic new role, not done in recent history.

The officials spoke on condition of anonymity because the announcement has not yet been made. The forces are expected to be used to support border patrol agents, with logistics, transportation and construction of barriers.