Rudy Giuliani, the personal lawyer of U.S. President Donald Trump, says U.S. sanctions are causing economic pain on Iran that will eventually lead to the downfall of the Tehran government.

"I don't know when we're going to overthrow them," Giuliani said at an Iran Uprising Summit held by the Organization of Iranian-American Communities in New York on September 22.

"It could be in a few days, months, a couple of years. But it's going to happen," Giuliani told the group, which opposes the government in Tehran.

The State Department has said Giuliani does not speak for the administration on Iran. Giuliani said he was speaking in his own capacity at the event and not an official representative of the president.

The U.S. administration has consistently said it is not seeking "regime change" in Tehran, only a "change in behavior."

Trump has accused Iran of supporting militant activity in the region and of trying to develop nuclear weapons, charges Tehran has denied.

The president in May pulled out of the 2015 nuclear deal that Iran signed with world powers and last month began reimposing sanctions against Tehran. The deal eased some sanctions in return for curbs on Iran's nuclear program.

The sanctions have worsened Iran's economic crisis and caused a major loss in the value of the country's currency, the rial, and has helped spur major street demonstrations in the country.

"The people of Iran obviously have now had enough," Giuliani said. "The sanctions are working. The currency is going to nothing...these are the kinds of conditions that lead to successful revolution."

Based on reporting by Reuters