The US has announced more sanctions on Iran, a week after a US warship confiscated Iranian missile parts headed for Yemen.
US Secretary of State Mike Pompeo said the US was sanctioning Iran's Mahan Air for carrying weapons of mass destruction.
The US first imposed sanctions on Mahan Air in 2011, saying it provided financial and other support to Iran’s Revolutionary Guard Corps.
Mr Pompeo also announced the reintroduction of sanctions against the Iran Shipping Lines company, calling the lifting of sanctions under the 2015 nuclear deal "an enormous mistake".
E-Sail Shipping in Shanghai will also be subject to sanctions. Mr Pompeo said the company "knowingly transports illicit materials" to Iran.
The designations will come into effect on June 8, 2020.
The US has said the airline has clear links to Iran's Revolutionary Guard Corps and its shadowy international wing, the Quds Force.
Italy banned flights from the airline in November after bowing to US pressure to isolate Iran.
The sanctions signal a continuation of the US "maximum pressure" campaign against Iran.
"A long as its malign campaign continues, so will our campaign of maximum pressure," Mr Pompeo said.
He warned US citizens of the "massive" danger of travelling to Iran, saying they risked "kidnap, arrest and detention".
Iran-US relations sank to a new low last year after President Donald Trump abandoned a 2015 deal in which world powers agreed to lift sanctions on Tehran in exchange for limits on its nuclear programme.
But Mr Pompeo said a recent prisoner swap between the US and Iran would lead to a broader effort for the release of more Americans.
At the weekend, Iran freed a Chinese-American scholar from Princeton who had been held for three years on false espionage charges.
After the swap, the Iranians said the US was holding about 20 more of its citizens and wanted to work towards more swaps.
