The Obama administration said Thursday that a $400 million cash payment to Iran seven months ago was contingent on the release of a group of American prisoners.

It is the first time the U.S. has so clearly linked the two events, which critics have painted as a hostage-ransom arrangement.

State Department spokesman John Kirby repeated the administration's line that the negotiations to return the Iranian money — from a decades-old military-equipment deal with the U.S.-backed shah in the 1970s — were conducted separately from the talks to free four U.S. citizens in Iran.

But he said the U.S. withheld the delivery of the cash as leverage until Iran permitted the Americans to leave the country.

Speaking on CNN Thursday night, Kirby pushed back at those who interpreted what he said today as confirmation that the U.S. paid 'ransom' to Iran.

'First of all this is Iran's money,' he said. 'No. 2 I think the way ransom works is you have to pay first and then you get your hostages back, and that's not what happened here.'

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Admission: John Kirby, the State Department spokesman, said Thursday that paying $400 million to Iran had been 'contingent' on release of prisoners held by the regime

Four Iranian hostages were released on January 17, including a journalist, a pastor and a U.S. Marine, in a cash deal that Republicans are describing as a quid-pro-quo

Pastor Saeed Abedini had linked the two events. He said that as the prisoners waited for hours at an airport to leave Iran

Iranian state television broadcast this image of a shipping pallet stacked with cash in February, a month after the January 17 drop

Both events occurred Jan. 17, fueling suspicions from Republican lawmakers and accusations from GOP presidential nominee Donald Trump of a quid pro quo that undermined America's longstanding opposition to ransom payments.

Trump created a firestorm by suggesting he had seen footage of the cash drop, something he later had to retract, though he may have inadvertently been right.

Responding to the admission, Republican Senator Tom Cotton of Arkansas issued a withering statement, dripping with sarcasm and a warning that it could be open season now on the US with regards to terrorist ransoms.

'The Merriam-Webster dictionary defines ransom as 'money that is paid in order to free someone who has been captured or kidnapped', said Cotton.

'President Obama, Secretary Kerry, and the rest of the Obama administration ought to write that definition down and consult it the next time they broker the release of hostages from our enemies so they don't have to spend so long explaining themselves afterwards.

'I dearly hope there is not a next time. But the president has greatly exacerbated the chance that there will be. Terrorists and our other enemies around the world now know that President Obama pays ransom for hostages.'

Iranian state-run media videotaped the arrival of the flight carrying the $400 million, judging from a documentary that aired the following month in the Islamic republic, which Dailymail.com reported on first.

The Iranian video was aired February 15 on the state-run Islamic Republic of Iran Broadcasting television network, as part of a documentary called 'Rules of the Game.'

A narrator, speaking in Persian, describes a money-for-hostages transaction over video clips of a plane on an airport tarmac in the dead of night and a photo of a giant shipping pallet stacked with what appear to be banknotes.

The federal government shipped what many are calling a ransom payment in Euros and other non-U.S. currencies.

The copy of the documentary footage DailyMail.com obtained is not of high enough quality to determine which nation's banknotes are depicted.

None of the footage is stamped with a date or time, making it impossible to know when it was shot.

And the broadcaster blurred out one portion of the screen, covering up something resting on top of the mountain of money.

But the documentary begins with a narration saying: 'In the early morning hours of January 17, 2016 at Mehrabad Airport, $400 million in cash was transported to Iran on an airplane.'

The film describes the Obama administration's prisoner swap and Iran's cash windfall from Tehran's point of view as 'a win-lose deal that benefits the Islamic Republic of Iran and hurts the United States,' according to two English-language translations DailyMail.com obtained.

The documentary described this plane as arriving in the dead of night with the money, exactly the scenario that Donald Trump was criticized for describing

Donald Trump linked his rival Hillary Clinton to the deal to pay back Iran, labeling it on Twitter a 'Scandal!'

Donald Trump had claimed to have seen footage of the plane carrying the $400 million to Iran, but then later retracted that statement - however he may have been right

It outlines what Iran's mullahs promoted at the time as a one-sided transaction loaded with perks for Tehran.

'The Islamic republic made an expensive offer to the equation: the release of seven Iranian prisoners in the United States, $1.7 billion, and the lifting of sanctions against 16 Iranians who were prosecuted by the U.S. legal system with the unjust excuse of sanctions violations,' the narrator intones.

'But this was not all the Iranians' demands. Lifting sanctions against Sepah Bank was added to Iran's list. All of this, in return for the release of only four American citizens: a win-lose deal that benefits the Islamic Republic of Iran and hurts the United States.'

Kirby spoke a day after The Wall Street Journal reported new details of the crisscrossing planes on that day.

U.S. officials wouldn't let Iran bring the cash home from a Geneva airport until a Swiss Air Force plane carrying three of the freed Americans departed from Tehran, the paper reported.

The fourth American left on a commercial flight.

RANSOM OR NOT RANSOM? A TIMELINE OF EVENTS January 17: Four American hostages are freed from Iran. A plane carrying $400 million in money owed to the Islamic republic arrives. January 21: A Wall Street Journal report says the timing of the payment 'raises questions of ransom' February 15: A documentary airs in Iran that details a money-for-hostages transaction between the country and the United States. August 3: Donald Trump tweets that Hillary Clinton 'was the one who started talks to give 400 million dollars, in cash, to Iran. Scandal!' He also claims to have seen footage of the plane that held the cash. State Department spokesman John Kirby tweets that, 'Reports of link between prisoner release & payment to Iran are completely false.' August 4: Both President Obama and Josh Earnest say that the White House did not pay 'ransom' to Iran. August 5: The Dailymail.com publishes details about the documentary which seemingly shows the cash arriving in Iran. August 17: The Wall Street Journal publishes more details about the 'tightly scripted exchange' that was 'specifically timed.' August 18: Kirby says the U.S. withheld the delivery of the cash as leverage until Iran permitted the Americans to leave the country. Advertisement

Earlier this month, after the revelation the U.S. delivered the money in pallets of cash, the administration flatly denied any connection between the payment and the prisoners.

'Reports of link between prisoner release & payment to Iran are completely false,' Kirby tweeted at the time.

The money comes from an account used by the Iranian government to buy American military equipment in the days of the shah.

The equipment was never delivered after the shah's government was overthrown in 1979 and revolutionaries took American hostages at the U.S. Embassy in Tehran.

The two sides have wrangled over that account and numerous other financial claims ever since.

President Barack Obama has said his negotiators secured the U.S. a good deal on a busy diplomatic weekend that also included finalizing the seven-nation nuclear accord.

But he and other officials have consistently denied any linkage.

'We actually had diplomatic negotiations and conversations with Iran for the first time in several decades,' Obama said Aug. 5, meaning 'our ability to clear accounts on a number of different issues at the same time converged.'

'This wasn't some nefarious deal,' he said.

The agreement was the return of the $400 million, plus an additional $1.3 billion in interest, terms that Obama described as favorable compared to what might have been expected from a tribunal set up in The Hague to rule on pending deals between the two countries.

U.S. officials have said they expected an imminent ruling on the claim and settled with Tehran instead.

Some Iranian officials immediately linked the payment to the release of four Americans, including Washington Post reporter Jason Rezaian, who had been held in Iranian prisons.

Another of the prisoners, pastor Saeed Abedini, also had linked the two events. He said that as the prisoners waited for hours at an airport to leave Iran, a senior Iranian intelligence official informed them their departure depended on the plane with the cash.

U.S. officials had pinned the delays on difficulties finding Rezaian's wife and mother, and ensuring they could depart Iran with him.

Trump's campaign jumped to attention at news of a connection, linking what happened to Democratic nominee Hillary Clinton, as she's campaigned on the administration's triumphs.

'Today's admission by the State Department that they paid a $400 million ransom to release American hostages from Iran further cements Hillary Clinton's role in crafting disastrous policies that have led to a more dangerous world,' said Trump's senior communications adviser Jason Miller in a statement to reporters.

'Already under fire for lying to the American people about her illegal email server, Clinton is continuing to align herself with an Administration that has continually lied to Americans as well,' he continued.

'By helping put together a deal that ultimately sent $400 million to Iran that was likely used to fund terrorism, Clinton has proven herself unfit to be president of the United States,' Miller concluded.

House and Senate Republicans have peppered the Obama administration for more details about the transaction.

'For months, the president and his spokespeople denied that he had reversed decades of U.S. policy by ransoming the freedom of American citizens,' House Speaker Paul Ryan's spokesman Doug Andres said in a statement, noting how today Kirby 'finally admitted it.'

'As the president once acknowledged, paying random 'risks endangering more Americans and funding the very terrorism that we're trying to stop,'' Andres added.

'He owes the American people a full and honest accounting of the ransom payment made in January,' Andres said.

Additionally, Sen. Mark Kirk, R-Ill., said Thursday he sees congressional hearings 'as the only way for the American people to fully know whether their tax dollars went directly to Iran's terrorist Islamic Revolutionary Guard Corps.'

Kirk is chairman of the Senate Banking national security subcommittee. No hearing dates have been set. Congress returns from a lengthy recess after Labor Day.

The House Financial Services Committee hasn't yet decided whether to hold hearings.

Rep. Sean Duffy, R-Wis., who chairs the Financial Services oversight and investigations subcommittee, asked the Treasury and Justice departments and the Federal Reserve last week to provide all records related to the $400 million payment as well as the names of government officials who authorized the payment and those who objected to the cash transfer.