The move came a day after the Trump administration told the Congress that Iran is complying with the nuclear deal signed two years ago with the US and other world powers, and as such would continue to be exempted from American sanctions.
However, the State Department today said "Iran's other malign activities are serving to undercut whatever positive contributions to regional and international peace and security were intended to emerge" from the nuclear deal.
"In response to these continued Iranian threats, the Administration today announces that it has designated 18 entities and individuals supporting Iran's ballistic missile programme and for supporting Iran's military procurement or Iran's Islamic Revolutionary Guard Corps (IRGC), as well as an Iran-based transnational criminal organisation and associated persons," State Department Spokesperson Heather Nauert said.
Ms Nauert also accused Iran of supporting radical groups such as Hezbollah, Hamas, and Palestinian Islamic Jihad "that threaten Israel and stability in the Middle East."
Iran continues to test and develop ballistic missiles in direct defiance of UN Security Council Resolution 2231, the spokesperson said.
On Monday, the State Department notified the Congress that the US continues to waive sanctions as required to continue implementing sanctions-lifting commitments in the Joint Comprehensive Plan of Action (JCPOA).
"The US will continue to use sanctions to target those who lend support to Iran's destabilising behavior and above all, the US will never allow the regime in Iran to acquire a nuclear weapon," the spokesperson said.
Ms Nauert said the US remains deeply concerned about "Iran's malign activities" across the Middle East which undermine regional stability, security, and prosperity.
Alleging that Iran has maintained its steadfast support for the Assad regime, despite Assad's atrocities against his own people, the State Department said Tehran also continues to provide the Houthi rebels in Yemen with advanced weaponry that threatens freedom of navigation in the Red Sea, has been used to attack Saudi Arabia, and is prolonging the Yemen conflict.
It also highlighted the range of malign activities by Iran that extend well beyond the nuclear realm.
"The President and the Secretary of State judge that these Iranian activities merely undermine the intent of the JCPOA, which was to contribute to regional and international peace and security.
"And as a result, the President, the Secretary of State, and the entire administration judge that Iran is unquestionably in default of the spirit of the JCPOA," said a senior administration official on anonymity.
"There have been a number of years of concessions to the Iranian regime, and the administration does not intend to overlook those any further. In previous years, US policy pertaining to Iran made the JCPOA the centerpiece of the US approach. And that narrow approach led us to overlook some of the broader, malign behaviors that the Iranian regime conducted, particularly in its region," the official said.
Moving forward, the administration intends to employ a strategy that will address the totality of Iran's malign behavior and not narrowly focus just on the Iranian nuclear agreement, the official added.
It has been a longstanding complaint that the previous administration allowed the nuclear deal to be the "tail that wags the Iran policy dog", the official said, adding that the Trump administration is determined to not repeat that mistake.
In the past, the official alleged, Iran had taken advantage of the previous administration's permissive view of the number of centrifuges that Iran is allowed to operate as part of its research and development plan.
"In concert with our European allies, we have determined that we need to approach those things more stringently," the official added.
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