President-elect Donald Trump has backtracked on the suggestion he would jail his Democrat rival Hillary Clinton if elected, now saying he has more important things to focus on.

Throughout his election campaign, the Republican hit out at Clinton over the investigation into her use of a private email server during her role as secretary of state, suggesting he would launch a fresh investigation if he won the White House.

However, he has now said pursuing a prosecution of his former rival is low down on his list of priorities, telling the Wall Street Journal: "It's not something I've given a lot of thought, because I want to solve health care, jobs, border control, tax reform."

During the second presidential debate, Trump stepped up his previous suggestions he would investigate Clinton, saying she would be in jail if he were president.

"I'll tell you what. I didn't think I'd say this, but I'm going to say it, and I hate to say it. But if I win, I am going to instruct my attorney general to get a special prosecutor to look into your situation, because there has never been so many lies, so much deception. There has never been anything like it, and we're going to have a special prosecutor," Trump said.

"It's just awfully good that someone with the temperament of Donald Trump is not in charge of the law in our country," Clinton responded.

"Because you'd be in jail," Trump shot back.