He said the release of 2,130 civilian prisoners, most of them Syrian but also including Turks and other foreign citizens, had begun in return. Two state-run Iranian television channels also reported that 48 Iranians had been freed in a swap.
There was no confirmation from the Syrian government, which has periodically freed hundreds of prisoners over the 21-month-old conflict in apparent concessions. But Damascus has always stressed such prisoners "do not have blood on their hands."
Syrian government forces have struck local deals with rebel groups to trade prisoners but the release announced on Wednesday would be the first time non-Syrians were freed in a swap.
Opposition groups accuse Assad of detaining tens of thousands of political prisoners during his 12 years in office and say those numbers have spiked sharply during the civil war.
Missing persons became a key issue when street protests against Assad first erupted in March 2011.
Turkey is one of Assad's fiercest critics, a strong opposition backer and proponent of international intervention. It has been highly critical of Iran's stance during the Syrian uprising, which has killed around 60,000 people according to a U.N. estimate.
Turkey, Gulf Arab states, the United States and European allies support the mainly Sunni Muslim Syrian rebels, while Shi'ite Iran supports Assad, whose Alawite minority is an offshoot of Shi'ite Islam.
A pro-government newspaper said on Dec. 31 that Syrian forces arrested four Turkish fighter pilots who were trying to sneak into a military airport with an armed group in the northern province of Aleppo.
State-run media did not mention the reported incident.