Republican presidential nominee Donald Trump speaks at the Merrill Auditorium on Aug. 4 in Portland, Maine. (Sarah Rice/Getty Images)

DES MOINES — Donald Trump accused President Obama of lying Friday about whether the administration paid Iran $400 million in ransom for U.S. prisoners, intensifying his charge even as he backed away from earlier claims that he had seen video footage of the exchange.

Footage of such an exchange does not appear to exist.

"We've just learned about a $400 million ransom payment. Now Obama said yesterday, ‘It has nothing to do with it.’ It's another lie. It's just like the Obamacare lie,” Trump said, referring to the Affordable Care Act during a campaign event in Des Moines. “It's just like so many other lies. It's another lie. Same day, just a coincidence right? Cash. Cash."

The Obama administration did in fact deliver $400 million in cash to Iran, which it announced earlier this year, as part of a $1.7 billion package that settles a previous financial dispute between the two countries. But that money was not, according to the administration, given to Iran in exchange for the prisoners; instead, their release came as a separate negotiation. Obama’s critics have seized on how the payment and the prisoner release were announced on the same day in January.

Obama has blasted people who accused him of paying a ransom for the prisoners, one of whom was Washington Post reporter Jason Rezaian: "We announced these payments in January, many months ago. They weren't a secret. This wasn't some nefarious deal," Obama said during a news conference Thursday.

Trump landed in hot water this week when he described in vivid detail video footage showing the money being delivered at a “top secret” location, leading to confusion and speculation that he had potentially seen such footage during a security briefing.

Such a video, however, does not exist. His spokeswoman later clarified that he had mistaken grainy footage on Fox News showing the prisoners being released in Geneva for footage of the financial payment.

“The plane I saw on television was the hostage plane in Geneva, Switzerland, not the plane carrying $400 million in cash going to Iran!” Trump tweeted Friday morning.

Trump has not yet begun receiving intelligence briefings.

Hundreds of people gathered at the Iowa Events Center to listen to Trump speak. There were already loud shouts of “Lock her up!” in the arena before he took the stage, which continued throughout the rally.

Trump tore into his Democratic rival, Hillary Clinton, during the rally.

"She's really pretty close to unhinged and you've seen it, you've seen it a couple times. … and she's like an unbalanced person," Trump said during the event  as the crowd raucously shouted to “lock her up.” Trump gave a thumbs up as the crowd chanted.

Trump also said at one point that electing Clinton would lead to “the destruction of our country from within.”

Indiana Gov. Mike Pence, Trump’s running mate, warmed up the crowd before the real estate mogul took the stage. He homed in on Clinton, knocking her for her use of a private email server during her tenure as secretary of state and mocking her speech at the Democratic convention.

"I had about as hard a time staying awake as her husband did. It wasn't just that it was long and it was late, it was just the same old same old,” he told the crowd, to loud cheers.

Trump also took aim at the media, which he accused of distorting his suggestion that a crying baby leave one of his events Tuesday in Ashburn, Va. He had initially encouraged the infant and his mother to stay despite the loud crying, before saying with a smile that "I was only kidding" and "you can get that baby out of here."

He addressed the flak, which drew numerous headlines, Friday: "I don't throw babies out. Believe me. I love babies. I love my children, I love babies. I don't throw babies out."

He added later: "You’ll hear everything very different from what we all know. Like the baby. Like that beautiful baby. I love that baby!"

Chris Ross, 53, said she is a moderate voter and remains on the fence over who to vote for. Ross, who works in a grocery business in Des Moines, is skeptical of Trump and unsure about his temperament.

"I don't think he's recognizing the gravity of the office he's running for," she said. "The thing that bothers me most is that he does not think before he speaks."

But she's not exactly a fan of Clinton's, either.

"I am concerned about having him representing the U.S." she said. "I have reservations about Hillary because she's been in politics 20-plus years. For him, he's a rich business executive. He's used to getting what he wants."

Phil Henry of Des Moines said that he became a Trump supporter when Sen. Ted Cruz (R-Tex.) dropped out of the race. He said that he initially thought Cruz was "more presidential.” But Henry, 62, is supporting Trump now because he thinks he’s a better option than Clinton.

"I almost thought it was like a joke" when Trump announced his candidacy, Henry said Friday. "I'd rather see Rand [Paul] than Trump running. He's got more quality going for him."

But: "I wish he'd keep his mouth shut more.”