US President Donald Trump has insisted he committed no wrongdoing but has the “absolute” power to pardon himself, echoing sweeping arguments put forth by his lawyer Rudy Giuliani on Sunday.

The remarks come as special counsel Robert Mueller’s investigation into alleged Russian meddling in the 2016 US election and possible illegal obstruction of that probe by the president has entered its second year.

Mr Giuliani told Reuters on Sunday the president cannot be indicted or subpoenaed and has the power to pardon himself, leaving impeachment by the US Congress likely the remedy for presidential misconduct.

“The constitution gave the president the right to pardon himself,” Mr Giuliani said, adding that Mr Trump would not need to because “he didn’t do anything wrong.”

Mr Trump said the same thing on Twitter on Monday, writing, “As has been stated by numerous legal scholars, I have the absolute right to PARDON myself, but why would I do that when I have done nothing wrong?”

As has been stated by numerous legal scholars, I have the absolute right to PARDON myself, but why would I do that when I have done nothing wrong? In the meantime, the never ending Witch Hunt, led by 13 very Angry and Conflicted Democrats (& others) continues into the mid-terms!

— Donald J. Trump (@realDonaldTrump) June 4, 2018

In another tweet he called Mr Mueller’s appointment “totally UNCONSTITUTIONAL.”

Mr Trump has denied he colluded with Russians or obstructed justice and repeated in tweets on Monday his frequent claim that the Mr Mueller investigation is a “witch hunt.”

Russia has denied US intelligence agencies’ assessment that Moscow sought to interfere with the 2016 U.S. election to boost Mr Trump’s prospects.

The Constitution is silent on the issue of whether the president’s broad power to grant pardons extends to himself, and some lawyers say that supports Mr Trump’s position.

“If there are any limits on the power, it’s got to be in the Constitution,” former lawyer with Justice Department office that handles pardons, Samuel Morison said. “It’s nowhere in the Constitution.”

But many legal experts disagree. Andrew Wright, a former associate counsel in the Obama White House, said allowing the president to pardon himself would be contrary to fundamental principles of the American legal system.

“One of the basic rules is that no man is a judge in his own case,” professor at Savannah Law School Mr Wright said.

Mr Trump’s tweet on Monday triggered swift political criticism.

“You can’t pardon yourself,” Democratic US Representative Ted Deutch said on Twitter. “Let me remind you of something, we don’t live in a monarchy and you are not a king.”

Many legal experts say the president’s actions could be considered obstruction if prosecutors can show he acted with “corrupt intent.”

Mr Mueller, who was appointed by Deputy Attorney General Rod Rosenstein in the wake of the May 2017 firing of FBI director James Comey, has so far secured five guilty pleas.

Among those who have pleaded guilty are former Trump national security adviser Michael Flynn and Rick Gates, a longtime business partner of Paul Manafort, the former Trump campaign chairman who has been indicted in the investigation.