President Donald Trump said Thursday he thinks the appointment of special counsel for the Russia investigation is bad for the United States.

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

Trump made his comments during a lunch with reporters and TV anchors.

"It also happens to be a pure excuse for the Democrats having lost an election that they should have easily won because of the Electoral College being slanted so much in their way. That's all this is. I think it shows division, and it shows that we're not together as a country. 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."

On Wednesday, Justice Department officials announced that Deputy Attorney General Rod Rosenstein had tapped former FBI Director Robert Mueller as special counsel, taking over the investigation into Russia's alleged meddling in the 2016 election.

After the announcement, the White House issued a measured statement on the president's behalf:

"As I have stated many times, a thorough investigation will confirm what we already know — there was no collusion between my campaign and any foreign entity. I look forward to this matter concluding quickly. In the meantime, I will never stop fighting for the people and the issues that matter most to the future of our country."

But Thursday morning, Trump tweeted a more aggressive tone, calling the investigation into potential ties between Russia and his presidential campaign a "witch hunt," a sentiment he reiterated later Thursday during a joint press conference with Colombian President Juan Manuel Santos.

@realDonaldTrump: This is the single greatest witch hunt of a politician in American history!

Trump also asked why no special counsel was appointed for what he called "all of the illegal acts" of Hillary Clinton's campaign and the Obama administration.

@realDonaldTrump: With all of the illegal acts that took place in the Clinton campaign & Obama Administration, there was never a special counsel appointed!

In a recent NBC News/Wall Street Journal poll, 78 percent of respondents said they would rather see the investigation led by an independent commission or special prosecutor, versus one led by Congress.

— NBC News and CNBC's Jacob Pramuk contributed to this report.