The remark was made by Nasser Kan'ani late Sunday, who was reacting to statements by an American official who denied the deal.
"From the viewpoint of the Islamic Republic of Iran, the issue of exchanging prisoners is a completely humanitarian issue, which must not be subject to political games," Kan'ani said.
The spokesman added, "Since last March, a written agreement has been signed [between the two sides] through an intermediary with regard to exchanging prisoners."
"An official representative introduced by the American side has also signed the agreement, but the deal has not been implemented so far by the US administration under various excuses," he said.
Kan'ani concluded by saying, "Indirect messages have been exchanged [between Iran and the US] during recent weeks to update that [agreement]."
The deal was announced earlier in the day by Iranian Foreign Minister Hossein Amir-Abdollahian, who confirmed that Tehran and Washington have reached an initial agreement to swap prisoners.
“We reached an agreement in recent days on the issue of prisoner swap,” Iran's top diplomat said, adding that if everything goes well on the American side, the exchange would take place soon.
"The ground for its implementation has been prepared now, and from our point of view, everything is ready while the US is currently working on the final technical coordination,” the top Iranian diplomat explained.
The original agreement on the exchange of prisoners was reached between Tehran and Washington in Vienna on the sidelines of negotiations concerning the 2015 nuclear deal, officially known as the Joint Comprehensive Plan of Action (JCPOA).
Tehran has repeatedly said it is ready for a prisoner exchange with the United States based on the agreement and independent of the nuclear deal, which the US unilaterally abandoned in May 2018 despite Iran's full and strict compliance.
MNA/Press TV