Media playback is unsupported on your device Media caption Donald Trump claims the Iranian military has a tape of the US transferring $400m (£305m) to Iran

US Republican presidential nominee Donald Trump has backtracked on a claim that he saw video footage of a US cash payment to Iran.

He made the claim at a rally. His team admitted it was incorrect, only for Mr Trump to repeat it at another rally.

The money was paid at the same time US hostages were freed, but the president said it was a payment linked to the landmark Iranian nuclear agreement.

Mr Trump said the video he saw was of the hostage transfer, not the payment.

The White House announced in January it was making payments to Iran - a total of $1.7bn (£1.3bn) to settle a decades-old dispute over a failed military equipment deal - as part of the nuclear accord.

A newspaper this week revealed that $400m of that was delivered in cash, flown to Iran at roughly the same time as four Americans were released in a prisoner exchange.

The timing of the transfer brought attacks from Republicans, including Mr Trump.

President Barack Obama denied any connection between the cash and the prisoner swap, saying: "We do not pay ransom for hostages." He said the payment had to be in cash because strict financial sanctions precluded other methods.

Analysis: Anthony Zurcher, BBC North America Reporter

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Being Donald Trump means never having to say you're sorry - or mistaken. The candidate has made a habit of steadfastly sticking by comments whose veracity, to put it mildly, has been called into question.

For instance, assertions that Muslim-Americans celebrated after 9/11, that neighbours didn't tell authorities they saw the San Bernardino shooters making bombs and that Mexico has a policy of sending criminals into the US have been roundly debunked by fact-checkers, yet all have been fixtures in Trump speeches.

This track record makes it noteworthy that on Friday morning Mr Trump backed away from his recent claims that he saw a video of Iranians unloading crates currency from a US plane.

Perhaps cooler heads in the Trump camp prevailed. Perhaps Mr Trump realised that his remarkably detailed misstatements were burying what could have been an effective campaign issue - the perception that the Obama administration was exchanging money for hostages.

It's become conventional wisdom that there isn't a tactical political advantage - on foreign affairs, Clinton emails, etc - that Mr Trump can't mishandle. Republicans can only hope Mr Trump's backtracking here is a sign of new, more disciplined candidate emerging.

However, the BBC's Barbara Plett Usher in Washington says it did not help that Iranian defence officials had described the money as a ransom payment.

Mr Trump insisted on Wednesday he had seen video showing the money being delivered.

His team on Thursday acknowledged this was not the case, saying Mr Trump was referring to cable news file footage of hostages being released.

But Mr Trump repeated his claim at another rally later on Thursday.

On Friday, his tweet was echoing the campaign team, saying: "The plane I saw on television was the hostage plane in Geneva, Switzerland, not the plane carrying $400 million in cash going to Iran!"

'Blank cheque'

Donald Trump has had a difficult week. His rival, Hillary Clinton, has seen a significant opinion poll boost since the Democratic convention.

Media playback is unsupported on your device Media caption Republican Congressman Mike Coffman airs anti-Trump advert

He has also run into trouble by rowing with the parents of a Muslim US army captain who was killed in Iraq and was criticised for calling Mrs Clinton "the devil".

A number of high-profile figures, including Republicans, have come out against him.

Republican Congressman Mike Coffman was one to air an anti-Trump advertisement.

Former director of the CIA, Michael Morell, not affiliated to either party, said in the New York Times that he would "do everything I can to ensure [Mrs Clinton] is elected our 45th president".

Citing Mr Trump's positions on Russia, Mr Morell called the New York billionaire an "unwitting agent" of Vladimir Putin.

Key national security figure endorsements

Endorsed Mrs Clinton

Gen John Allen, retired

Richard Armitage, former deputy secretary of state (Republican)

Gen Wesley Clark, retired, former head of Nato

Michael Morell, former CIA director

Leon Panetta, former defence secretary

Adm James Stavridis, retired, former head of Nato

Brent Scowcroft, former national security adviser (Republican)

Not voting for Mr Trump

William Cohen, former defence secretary (Republican)

Michael Hayden, former CIA director (Republican)

On Thursday, Republican House Speaker Paul Ryan told fundraisers the party had to protect its majority in Congress or "we could be handing President Hillary Clinton a blank cheque".

It echoed the "Let's not give Clinton a blank cheque" phrase used by Republicans in 1996 when it became clear Bob Dole would not defeat Bill Clinton.

However, Mr Trump's running mate, Mike Pence, stood firmly behind him on Friday, telling NBC: "Donald Trump and I are standing shoulder to shoulder to say to the American people, 'we can be strong again'."