President Donald Trump wants to use the military to secure the US-Mexico border until his promised wall is built.
Mr Trump said during a lunch with Baltic leaders that he has spoken with Defence Secretary Jim Mattis about the idea.
He called it a “big step”.
Mr Trump begrudgingly signed a spending bill last month that provided far less money for the wall than he wanted.
He has been complaining that US borders are too porous and immigration laws are too weak.