"Over the past few days, hundreds of millions of dollars entered the market through (CBI-linked) brokers and thwarted many of the plans of those trying to destabilize the foreign exchange market," Hemmati said in an Instagram posting.
The rial currency sank to its lowest-ever level on Tuesday before recovering slightly. It has been under pressure from US sanctions and the coronavirus crisis, Reuters wrote.
After saying on Friday that the CBI would not "'spray' its resources onto the market", Hemmati said that he did not mean the bank would hold back from supporting the rial.
"Our market intervention will be prudent and goal-oriented," he said.
The rial was trading at around 200,000 per US dollar on the unofficial market on Sunday, according to foreign exchange websites.
The currency gained slightly against the US dollar earlier, trading at around 192,000 per dollar on Friday, after falling to a historic low of 205,000 on Tuesday.
The official exchange rate is 42,000 rials per dollar and is used mostly for imports of state-subsidized food and medicine.