Donald Trump admitted Thursday that he knows he sometimes says the "wrong thing," but said he regrets his past mistakes that might have caused "personal pain" in the past.

"Sometimes, in the heat of debate and speaking on a multitude of issues, you don't choose the right words or you say the wrong thing. I have done that, and believe it or not, I regret it," Trump told the crowd. "And I do regret it, particularly where it may have caused personal pain. Too much is at stake for us to be consumed with these issues."

"But one thing I can promise you is this: I will always tell you the truth," he added.

The comment is startling given Trump's noted opposition to apologies. It was also his third speech this week in which he relied on a teleprompter, an aid he proudly rejected early in his campaign.

Trump also reverted to form by bashing the Obama administration over the revelation from the State Department that the $400 million payment to Iran was timed to guarantee the release of American prisoners, a move many Republicans immediately said amounted to a ransom payment in violation of U.S. law. He told the crowd that President Obama "openly and blatantly" lied that the money wasn't for the prisoners were being held there.

"Speaking of lies, we now know from the State Department, just announced that President Obama lied about the $400 million dollars in cash that was flown to Iran," Trump said. "He denied it was for the hostages, but it was ... He said we don't pay ransom, but he did. He lied about the hostages openly and blatantly just like he lied about Obamacare."

Trump was referring to Obama's oft-repeated line that individuals who liked their doctor would be able to keep their doctor, which was roundly derided after it became apparent that was not true.

The speech was the first by the real estate mogul since his campaign's shake-up in leadership, which saw senior advisor Kellyanne Conway become campaign manager and Stephen Bannon, the former head of Breitbart News, become the campaign's chief executive.