Iran said Sunday it had expressed readiness for a full prisoner exchange with the United States "with no preconditions" but that Washington was yet to respond.

"We said some time ago that we are ready to exchange all Iranian and American prisoners," ISNA news agency quoted government spokesman Ali Rabiei as saying.

"It now appears that America is more ready than before to end this situation," he added, noting that Iran was waiting for a reply. "Washington has been notified of our readiness and we think no mediator is needed."

The Islamic republic in December freed Xiyue Wang, a US academic, in an exchange for scientist Massoud Soleimani and said it was open to further swaps. Rabiei also expressed concern about the health of some Iranian prisoners detained in the United States and claimed they are not being treated well.

One of them is Sirous Asgari, an Iranian scientist infected with the novel coronavirus while in detention, according to the Iranian foreign ministry. A ministry spokesman said last week that "everything is prepared" and declared "he will soon return to Iran" without elaborating further.

Iran is holding US citizens Siamak Namazi, convicted on charges that include espionage, his father Baquer and environmental expert Morad Tahbaz. According to the US State Department, Iran temporarily released US Navy veteran Micheal White on March 19.

Both countries have called for releasing prisoners over the virus outbreak. Iran is battling what is the Middle East's most deadly outbreak, while the US has reported the highest total number of virus deaths worldwide.