U.S. President Donald Trump on Friday backtracked from his suggestion a day earlier that American troops sent to the U.S. border with Mexico would be free to fire on migrants who throw rocks at them, saying that rock-throwers would only be arrested.

"They won't have to fire. What I don't want is I don't want these people throwing rocks," Trump told reporters outside the White House. "If they do that with us, they're going to be arrested for a long time."

Trump's rhetoric on shooting migrants drew criticism from human rights groups that said he was stoking fear ahead of next week's congressional elections. Calling migrants a national security threat "is as absurd as it is cruel," advocacy group Human Rights First said in a statement.