The U.S. dollar and other major currencies have witnessed a notable rise on the Tehran currency exchange market this week. The dollar’s gain has been about 10 percent.

As a reaction the chief of Iran’s central bank sounded a warning, that this trend will not necessarily stay, and people should not take risks with their money.

Iran’s currency has had a roller-coaster ride in the past one year; with steady declines to steep lows in September and then a partial rebound since then.

One year ago, the rial was trading at around 40,000 to the dollar, when U.S. President Donald Trump signaled that he intended to pull his country out of the 2015 nuclear deal with Iran.

Market sentiment and popular fears about an impending economic downturn caused the rial to steadily fall. To protect their money people began converting their local currency primarily into dollars.

The decline took the rial to as low as 180,000 to the dollar until in September government measures, including restricting trading and arresting dealers brought the dollar down to around 100,000 rials.

On Tuesday and Wednesday, the U.S. currency again rose above 120,000 rials. On Thursday, the rate came down a bit, but it still traded close to 120,000 rials.

The chief of central bank, Abdolnasser Hemmati in post on Instagram tried to pin the blame on profiteers and opportunists, but many market observers did not believe that the government could the exchange rate low, given the impact of sanctions reimposed by the United States and the decline in Iran’s oil revenues.