US imposes sanctions on Iranian missile firms

Treasury Secretary Steven Mnuchin linked Thursday's measure to recent anti-government protests, arguing that Iran ought to spend more on public welfare rather than banned weapons.

"These sanctions target key entities involved in Iran's ballistic missile programme, which the Iranian regime prioritises over the economic well-being of the Iranian people," Mnuchin said.

"As the Iranian people suffer, their government and the IRGC fund foreign militants, terrorist groups, and human rights abuses," he added.

"The United States will continue to decisively counter the Iranian regime's malign activity, including additional sanctions targeting human rights abuses.

"We will not hesitate to call out the regime's economic mismanagement, and diversion of significant resources to fund threatening missile systems at the expense of its citizenry."

The five designated companies are all subsidiaries of Iran's Shahid Bakeri Industrial Group (SBIG).

Under the sanctions, any assets that the firms hold in places under US jurisdiction will be frozen and US citizens are forbidden from doing business with them. Foreign institutions who work with the companies could be locked out of the US financial system.

Earlier, the State Department had warned that Iranian officials involved in the arrest or killing of protesters would be held to account.

"We condemn in the strongest possible terms the deaths to date and the arrests of at least one thousand Iranians," spokeswoman Heather Nauert said.

"We have ample authorities to hold accountable those who commit violence against protesters, contribute to censorship, or steal from the people of Iran," she said.

"To the regime's victims, we say: 'You will not be forgotten.'"

At least 21 people have been killed and hundreds arrested in Iran during a week of anti-government protests over economic woes and official corruption. 

Washington, a long-standing foe of Tehran, has stood up for the protesters' right to be heard, and Nauert has now gone further in endorsing what she said were their demands.

"We support these legitimate aspirations of the Iranian people, and call on the government to allow the free exchange of ideas and information," she said.

"All of us should be able to enjoy the same basic economic and political freedoms, including the right to peaceful demonstration."

But Iranian Ambassador Gholamali Khoshroo has complained that Washington is intervening in Iran's internal affairs "in a grotesque way" when commenting on the anti-government protests. 

In a letter to UN officials, Khoshroo said Trump and Vice President Mike Pence were personally stirring up trouble.

"The President and Vice-President of the United States, in their numerous absurd tweets, incited Iranians to engage in disruptive acts," the ambassador wrote to the UN Security Council President and UN Secretary-General Antonio Guterres.

Trump has unleashed a series of tweets in recent days backing the protesters, saying Iran is "failing at every level" and declaring that it is "time for change" in the Islamic Republic.

"Such respect for the people of Iran as they try to take back their corrupt government," he tweeted on Wednesday. "You will see great support from the United States at the appropriate time!"

Iranian officials now claim to have the crisis under control and state television is carrying footage of pro-government counter demonstrations in several cities.

Agencies contributed to this report