Iran's foreign ministry spokesman said on Monday that a prisoner swap with the United States was on the agenda in parallel with the nuclear talks in Vienna.

"This issue is currently on the agenda in parallel with the Vienna talks.... But it seems that the US has not made a decision on it. Perhaps it is waiting for the results of the talks," said Saeed Khatibzadeh.

This is the first time that an Iranian official says official talks over foreigners and dual nationals detained in Iran with the United States have been on the agenda in Vienna. Tehran has refused to directly negotiate with Washington since nuclear talks began last April in Vienna.

Iran is holding several Western prisoners in what human rights organizations have dubbed hostage diplomacy. As in past instances, Tehran is demanding the release of Iranian detained in the US for breaking sanctions laws and related offenses.

European powers, the European Union and Russia are shuttling between the two sides, while there have been more calls in Iran to negotiate directly with the US.

Khatibzadeh also said that the nuclear talks have not “reached a dead end.” Ten months after negotiations began still major issues of which US sanctions should be lifted and how Iran should return to its obligations under the 2015 nuclear agreement remain unresolved.