The United States says it is about to re-impose sanctions on Iran after President Donald Trump pulled out of the 2015 Nuclear deal in May.
Today's tranche of sanctions - the first of two sets, with others coming into effect on 4 November - would affect the purchase of US dollars, trade in gold and certain other metals, as well as aviation and the car industry.
In May, the US pulled out of the 2015 deal between world powers and Tehran under which international sanctions were lifted in return for curbs on its nuclear programme.
The US has told other countries they must halt imports of Iranian oil starting in early November or face financial measures.
Mr Trump had denounced the deal reached under his White House predecessor, Barack Obama, as one-sided in Iran's favor.
Iranian President Hassan Rouhani said last week that Mr Trump's repudiation of the deal was illegal and Iran would not yield to Washington's renewed campaign to strangle Iran's vital oil exports.
The Iranian currency has lost about half of its value since April because of a weak economy and heavy demand for dollars among Iranians who fear the effects of sanctions, prompting Iran to ease foreign exchange rules.
Secretary of State Mike Pompeo on Sunday said the sanctions were "an important part of our efforts to push back against Iranian malign activity".
Protests broke out on Sunday for a sixth night in Iranian cities, including Kazeroon in the south, according to social media. Authorities reported the first fatality among protesters, with the shooting of a man in Karaj, west of Tehran. But they denied security forces were involved, Iranian news agencies reported.
The protests have often begun with slogans against the high cost of living and alleged financial corruption but quickly turned into anti-government rallies.
Mr Pompeo said it would require "enormous change" by Iran to get out from under renewed U.S. sanctions. "They have got to behave like a normal country," he said, describing Iranian leaders as "bad actors."
He alluded to Trump's suggestion last week of the potential for future negotiations with Tehran, a notion that senior Iranian officials quickly rejected.
"We are happy to talk if there's an arrangement that is appropriate, that could lead to a good outcome," he said.
"Perhaps that will be the path the Iranians choose to move down with. There's no evidence to date of their desire to change to change their behavior."
- Reuters