President Donald Trump said on Monday he wants to deport some violent criminals who are U.S. citizens to Salvadoran prisons, a move that experts said would violate U.S. law.

Trump's comments marked the clearest signal yet that the U.S. president is serious about deporting naturalized and U.S.-born citizens, a proposal that has alarmed civil rights advocates and is viewed by many legal scholars as unconstitutional.

Trump said he would only go through with the idea if his administration determined it was legal. It was not clear what level of due process an American would receive before being deported to a country Washington has previously accused of serious human rights abuses, including harsh and arbitrary detentions.