The Biden administration has issued a waiver to allow banks to transfer $6 billion in restricted Iranian funds to Qatar without fear of sanctions -- a key step in a deal to free five Americans who have been deemed wrongfully detained in Iran by the US State Department.

The process to bring the Americans home began to move forward in mid-August with the release of four Americans into house arrest. The issuance of the waiver -- which the administration informed Congress about on Monday -- is the clearest sign yet that the process may be reaching its end stages.

In the notice to Congress -- a copy of which was obtained by CNN -- Secretary of State Antony Blinken confirmed that the US has committed to allow the transfer of the $6 billion held in restricted South Korean accounts to restricted accounts in Qatar to be used for humanitarian goods. Qatar will oversee the disbursal of those funds.

"The transfer requires the involvement of financial institutions from Germany, Ireland, Qatar, the ROK, and Switzerland," he wrote. The waiver, which Blinken approved on Friday, will allow those institutions to transfer the money to the accounts in Qatar without worry of invoking US sanctions. The waiver was first reported by the Associated Press.

Blinken also confirmed the prisoner swap component to the deal, noting that the US "has committed to release five Iranian nationals currently detained in the United States."

The development is likely to be welcome news to the families of the Americans involved in the deal -- Siamak Namazi, Morad Tahbaz, Emad Shargi, and two other Americans who have not been publicly identified -- as it signals their nightmare may be coming to an end. Namazi, Tahbaz, and Shargi have all been detained in Iran for years.

It is also likely to face opposition from some Republicans in Congress as well as some of the GOP presidential nominees who spoke out when the contours of the prospective deal were reported last month.

CNN reported on those details following the release of Namazi, Tahbaz, Shargi and a fourth American into house arrest in mid-August. A fifth American was already on house arrest.

At the time, a source familiar with the negotiations described the development as "an encouraging step," noting that there's "a roadmap that has basically been agreed." However, they said that "there's a number of things here that that still need to be worked out" in the prospective deal.

"There's kind of a step-by-step process that's going to unfold. So, the first step is getting our people out of prison," the source said.

"Then there will be arrangements in place we've agreed to do some things, Iran has agreed to do some things that will eventually lead to the Americans coming home," they said.

"It's going to be a period of weeks" before the five Americans could be back in the US, the source said at the time, noting a September timeframe.

The potential breakthrough came after more than a year of indirect negotiations between Washington and Tehran.