Donald Trump has been describing in detail at voter rallies a shocking video made by the Iranian military of piles of US money on pallets on a airport tarmac. The problem is no one knows of any such footage, and his own campaign denies that the candidate has ever seen such a video.

Trump has been trying to score points on information reported by the Wall Street Journal that the US turned over $400m (£300m) in cash to the Iranians early this year just as four American hostages were released. American officials have denied the money was a ransom payoff, saying that it was the first installment of $1.7bn (£1.28bn) the US has agreed to pay to settle a failed arms deal dating back to 1979.

Trump has set the scene at his rallies for this dramatic American payoff "embarrassment" as bold Iranian troops filmed the US cash being delivered to Iran.

"I saw $400m — different currencies, they probably don't want our currency — being flown to Iran," Trump said in a videotaped speech to a crowd of nearly 2,000 in Portland, Maine, Thursday (4 August). "I mean, folks, what is going on here?" he asked.

"It was interesting because a tape was made. Right? With the airplane coming in — nice plane — and the airplane coming in, and the money coming off, I guess. Right? That was given to us — has to be — by the Iranians. And you know why the tape was given to us? Because they want to embarrass our country. They want to embarrass our country. And they want to embarrass our president because we have a president who's incompetent.

"I mean, who would ever think they would be taking all of this money off the plane and then providing us with a tape? It's only for one reason. And it's very, very sad."

Trump first mentioned this footage from the Iranian government at a rally the previous day in Daytona Beach, Florida.

"I'll never forget the scene ," Trump said then. "Iran — I don't think you've heard this anywhere but here — Iran provided all of that footage, the tape of taking that money off that airplane.

"Here's the amazing thing. Over there, where that plane landed, top secret, they don't have a lot of paparazzi. You know, the paparazzi doesn't do so well over there, right? And they have a perfect tape done by obviously a government camera, and the tape is of the people taking the money off the plane, right?

"That means that in order to embarrass us further, Iran sent us the tapes, right? It's a military tape. It's a tape that was a perfect angle, nice and steady. Nobody getting nervous because they're going to be shot because they're shooting a picture of money pouring off a plane."

Senior US officials involved in the Iranian negotiations have all denied knowledge of any such tape. There was initially a fear that Trump had spilled classified information since he now receives weekly classified briefings as a presidential candidate — and at one point he called the video "top secret." But sources denied there was any such classified video.

Trump spokeswoman Hope Hicks told the the Washington Post and ABC News that the video was actually footage of a private plane landing in Geneva, Switzerland, in January with the American hostages who had just been released by Iran. She said it was the footage used in every broadcast on American media, including Fox News, where Trump watched it.

Trump, however, described scenes not found on that footage.

Trump repeated his story about the video at the Maine rally after his campaign denied that such footage existed when approached by the press after the Florida rally.

Early in his primary campaign Trump claimed to have seen a video of "thousands and thousands" of Muslims cheering on rooftops in New Jersey after the 9/11 terrorist attacks. No video matching that description has ever surfaced.