Immigrant rights advocates said the two memos signed by Kelly mark a major shift in U.S. immigration policies by dramatically expanding the scope of enforcement operations.

The new procedures would allow authorities to seek expedited deportation proceedings, currently limited to undocumented immigrants who have been in the country for two weeks or less, to anyone who has been in the country for up to two years.

Another new provision would be to immediately return Mexican immigrants who are apprehended at the border back home pending the outcomes of their deportation hearings, rather than house them on U.S. property, an effort that would save detention space and other resources.

The guidelines also aim to deter the arrival of a growing wave of 155,000 unaccompanied minors who have come from Mexico and Central America over the past three years. Under the new policies, their parents in the United States could be prosecuted if they are found to have paid smugglers to bring the children across the border.