The currency dropped to about 22,300 rials versus the dollar, Iran's Mehr News Agency reported. Persian-language currency tracking website Mesghal said the rate was about 21,850.

On Monday, the rial had tumbled to around 21,510 from its Sunday level of 20,440 after the central bank said it would change the currency's official exchange rate, prompting fears of another devaluation.

Central bank governor Mahmoud Bahmani said he would announce a change to the government's "reference rate" of 12,260 rials to the dollar "within the next 10 days". Iranian media speculated the new reference rate might be between 15,000 and 16,000 rials.

Most Iranians are unable to obtain dollars at the official rate and must instead use the free market, which is much more expensive. The rial has been under pressure this year because of international sanctions against Iran's economy imposed over its disputed nuclear programme.