Officials say there are more than 1,000 legal battles still to settle and says more payments to Iran are possible

The Obama administration paid Iran nearly $2billion in a 'ransom payment' to release U.S. prisoners after at least two years of secret talks between Washington and Tehran.

Five prisoners were freed by Iran in January this year, with a $1.7billion payment heading from the U.S. to the Islamic republic that day, according to official documents obtained by the Washington Free Beacon.

At least two years of secret talks led to the deal that officials claim is a settlement relating to one of more than 1,000 long-standing legal disputes that began after the 1979 Iranian Revolution.

Scroll down for video

The Obama (left) administration paid Iran nearly $2billion in a 'ransom payment' to release U.S. prisoners after at least two years of secret talks between Washington and Tehran. Right, Iranian President Hassan Rouhani

Five prisoners (including Washington Post journalist Jason Rezaian) were released by Iran in January this year, with a $1.7billion payment heading from the U.S. to the Islamic republic that day

Five U.S. citizens imprisoned in Iran - Washington Post journalist Jason Rezaian, pastor Saeed Abedini, former U.S. Marine Amir Hekmati, Matthew Trevithick and Nosratollah Khosravi-Roodsari - were released in a landmark prisoner swap in January.

In return, seven Iranian detainees in American were freed, although none returned to Iran.

It later emerged that $1.7billion was sent to Tehran that day, with critics branding the money a 'ransom payment'.

Republican Congresman Michael Pompeo asked the State Department to explain the payment, and has finally received a response.

The letter does not address allegations that the payment related to the release of the prisoners, but does say that the Obama administration first began talks with Iranian officials over outstanding legal claims leveled against the U.S. by Iran in 2014.

These date back to the Iranian Revolution in 1979, which led to the U.S. cancelling an arms deal and eventually ended with the Iranian hostage crisis at the U.S. embassy in Tehran.

Five U.S. citizens imprisoned in Iran - Rezaian, pastor Saeed Abedini (left), former U.S. Marine Amir Hekmati (right), Matthew Trevithick and Nosratollah Khosravi-Roodsari - were released in a landmark prisoner swap

Trevithick (right), the co-founder of a humanitarian crisis research center, had traveled to Iran in September for a four-month language program at an institute associated with Tehran University

The legal row over the scrapped arms deal led to more than 1,000 claims against the U.S., with American officials keen to settle as many of those out of court as possible.

Many of them are still in the process of being settled and it is just one of these disputes that the State Department claims led to the $1.7billion payment.

The response says that there could yet be more payments from Washington to Tehran as more legal tussles are brought to a close.

Republican Congresman Michael Pompeo asked the State Department to explain the payment.

The secret talks between the two countries were underway in June 2014 at the latest, and continued through 2015 until the prisoner swap in 2016.

'We are confident that this was a good settlement for the American taxpayer,' the State Department said.

'The United States is continuing to vigorously litigate these claims at the (Hague's Iran-U.S. Claims) Tribunal, but is also open to discussing further settlements of claims with Iran, as we have done throughout the life of the Tribunal, with the aim of resolving them in furtherance of U.S. interests,' the letter states.

'It would not be in the interest of the United States to discuss further details of the settlement of these claims in an unclassified letter due to the ongoing litigation at the Tribunal.

'However, we would be prepared to provide a closed briefing on such issues if it would be useful to there.'

The settlement in January included a $400million payment plus $1.3billion in interest, all from the taxpayer's pocket.

'When Iran releases American hostages, and then, on that same day, President Obama announces he is paying Iran $1.7billion, Congress of course has to ask the hard questions,' a source told the Free Beacon.

'And when the Obama administration admits that over $1billion in taxpayer money is going to the Iranian regime, Congress is obligated to respond.

'The State Department has ducked and dodged–providing a history lesson on international tribunals, focused on actions decades ago, instead of addressing dangerous misdeeds that were potentially just committed. That is suspicious.'