Tensions look set to continue rising between Tehran and Washington after Iran's leader announced a partial withdrawal from the 2015 nuclear deal.
For more on this and other news around the world, let's turn to Hong Yoo.
So Yoo, how is the U.S. responding to Iran's announcement?
Very strongly, Mark.
U.S. President Donald Trump issued an executive order on Wednesday announcing new sanctions will be imposed on Iran's steel, aluminum, copper and iron sectors, the key foreign currency earning sectors for Iran's economy.
Iran is already known to be economically crippled, its currency value plunging to record lows and a soaring annual inflation rate, due to the U.S. sanctions on their oil exports.
Yet these new sanctions will be "the most powerful maximum pressure campaign ever witnessed" targeting Iran's largest non-petroleum-related sources of export revenue, according to a statement from President Trump.
The economic crisis increased internal pressure on Iran's President Hassan Rouhani to take the counter action of partially withdrawing from the 2015 nuclear agreement.
"The JCPOA is here and it remains in place. But today we have shown the flipside of the JCPOA coin. This is the same JCPOA that states if the other parties are failing to meet their obligations, then we can also reduce our obligations in the deal. Today, we are announcing a reduction of our obligations under the JCPOA. We are not leaving the JCPOA."
The measures include removing caps on uranium enrichment levels, and resuming work on its Arak nuclear facility.
The move comes a year after the U.S. unilaterally withdrew from the deal, despite the strong objections of other signatories.