Trump to Muir: Special counsel 'hurts our country terribly' Robert Mueller was appointed Wednesday to lead the investigation.

 -- President Donald Trump doubled down on his criticism Thursday of the appointment of a special counsel to investigate Russian interference in last year's presidential election, telling ABC News' David Muir the action hurts the United States 'terribly.'

The comments came during a lunch with television network anchors at the White House Thursday as he was asked about the selection of former FBI Director Robert Mueller to lead the inquiry.

Muir asked the president what he’ll say to leaders around the world on his first foreign trip who are watching the headlines here in the United States and how he'll answer when asked if he supports the idea of a special counsel and if he was surprised by the move.

The president answered that he believed it was harmful.

“I believe it hurts our country terribly, because it shows we're a divided, mixed-up, not-unified country," said Trump.

"We have very important things to be doing right now, whether it's trade deals, whether it's military, whether it's stopping nuclear -- all of the things that we discussed today," he added. "And I think this shows a very divided country."

The remarks echo sentiments conveyed by Trump in a pair of tweets Thursday morning. After the president was reported to have a measured response to the news Wednesday, he lashed out online, calling the probe a "witch hunt."

"This is the single greatest witch hunt of a politician in American history!" tweeted Trump, who went on to note in an additional post that a special counsel was not appointed to investigate "the illegal acts that took place in the Clinton campaign & Obama Administration."

The president did not provide evidence of such acts' existence.

At the lunch, Trump portrayed the investigation as one driven by the Democratic party in response to his election victory, saying it was "a pure excuse for the Democrats having lost an election that they should have easily won."

"I think it shows division and it shows that we're not together as a country," continued Trump. "And I think it's a very, very negative thing. And hopefully, this can go quickly, because we have to show unity if we're going to do great things with respect to the rest of the world."

Watch “World News Tonight with David Muir” live from Washington, DC Thursday at 6:30 pm ET.