Iran may have received an additional $33.6 billion in secret cash and gold payments facilitated by the Obama administration between 2014 and 2016, according to testimony provided before Congress by an expert on last summer’s nuclear agreement with Iran.

Between January 2014 and July 2015, when the Obama administration was hammering out the final details of the nuclear accord, Iran was paid $700 million every month from funds that had previously been frozen by U.S. sanctions.

A total of $11.9 billion was ultimately paid to Iran, but the details surrounding these payments remain shrouded in mystery, according to Mark Dubowitz, executive director at the Foundation for Defense of Democracies.

In total, "Iran may have received as much as $33.6 billion in cash or in gold and other precious metals," Dubowitz disclosed.

New questions about these payments are emerging following confirmation from top Obama administration officials on Thursday that it was forced to pay Iran $1.7 billion in cash prior to the release of several U.S. hostages earlier this year. The administration insisted that cash had to be used for this payment.

Top administration officials were adamant that the cash payments were the best way to ensure that Iran got immediate access to this money due to its ongoing difficulty accessing international funds still sanctioned by the West.

Lawmakers and others are now pressing the administration to disclose how a slew of other payments to Iran were made in the years leading up to the final nuclear accord.

"In July, the Associated Press cited U.S. officials who estimated that Iran ‘brought home less than $20 billion.’ Were these funds repatriated to Tehran in cash or in gold and precious metals? Through the formal financial system? Or through some combination?" Dubowitz asked in his testimony before the House Financial Services Committee.

"The administration should also clarify if the $20 billion dollars is inclusive of the $11.9 billion in [Joint Plan of Action] funds, or if the $20 billion was in addition to the $11.9 billion," he said. "Either way, it is important to understand how funds were sent. The worst-case scenario here is that Iran may have received as much as $33.6 billion in cash or in gold and other precious metals."

At least some of this money was likely sent in cash and other assets, according to Dubowitz.

The Obama administration was forced to disclose on Thursday that current sanctions and banking restrictions prohibited it from transferring funds to Iran via electronic methods.

The cash payment of $1.7 billion earlier this year was the easiest way to ensure Iran got immediate access to the money, according to these officials.

"Iran had to have it in cash," Paul Ahern, assistant general counsel for enforcement and intelligence at the Treasury Department, told lawmakers. "Iran was very aware of the difficulties it would face in accessing and using the funds if they were in any other form than cash, even after the lifting of sanctions."

A cash delivery "was the most reliable way that they received the funds in a timely manner and it was the manner preferred by the relative foreign banks," Ahren said.

Given the situation, it is likely that the multiple past payments to Iran were conducted in a similar fashion, according to Dubowitz.

"If the White House could only send cash to Iran from the start of the JPOA period through the Tribunal payment that could amount to a grant total of 33.6 billion," he said. "Did any of this money go through the formal financial system? If so, the administration is not being truthful about the 1.7 billion. If many billions arrived in Iran on pallets [of cash] this would be a pretty astounding revelation."

Michael Rubin, a former Pentagon official and expert on rogue regimes, said that cash payments of this nature are "highly irregular."

"There’s no reason it needed to be paid now. After all, successive administrations, both Democratic and Republican, have delayed payments so as to avoid funding Iranian terrorism," Rubin said. "Likewise, if the United States freezes accounts linked to al Qaeda or Hamas, releasing it and saying, ‘It’s their money anyway,’ would not be a tenable explanation. Cash payments are highly irregular."

The Iranians have been clear that they "perceived the payment to be a ransom" despite the administration’s protestations, Rubin explained.

"Not only has the delivery of the millions of dollars been perceived as a ransom, provided as an incentive to seize more hostages …. but because the money was delivered in cash the payment bolstered the strength of the Islamic Revolutionary Guard Corps and augmented its ability to finance and conduct terrorism," he said.