The US has levelled sanctions against a Yemeni network that it claims was cooperating with Iran's Revolutionary Guard to illicitly transfer tens of millions of dollars to Yemen's Houthi rebels.
At the same time, the Biden administration on Thursday also announced it was lifting sanctions on three former Iranian oil executives and two companies that it said had been involved in banned petroleum sales, saying the U.S. had "verified a change in status or behaviour" on their part.
Neither the State Department nor the Treasury Department would elaborate further on the reason for the de-listings.
The departments of State and Treasury announced both moves in simultaneous statements that come as the administration is trying both to press the Iranian-linked Yemen rebels into peace talks for the war in Yemen, and close a deal returning the United States and Iran to an accord on Iran's nuclear programme.
The money moving through the alleged Houthi financing network came from sales of Iranian petroleum and other commodities throughout the Middle East, Secretary of State Antony Blinken said.
International officials and analysts say Iran has increased its material support to Yemen's Houthi rebels as the war in the Arab nation passes the six-year mark. A Saudi-led coalition is trying to hold off the Houthis, who seized the country's capital and are waging an offensive now to capture a major northern city, in defiance of US and UN calls for a ceasefire.
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The new US action designates 11 Yemeni individuals, alleged front companies and intermediaries and vessels involved in what it said were the illicit transfers.
The 11 included Jami' 'Ali Muhammad, a Houthi and alleged Iranian Revolutionary Guard associate who the United States says helped procure vessels, facilitate shipments of fuel, and transfer funds for the benefit of the Houthis."
The 2015 nuclear deal is based on Iran limiting development of its nuclear program in return for the US and others lifting sanctions against Iran. Ongoing talks in Vienna have focused partly on timing of the US lifting sanctions and Iranians returning to compliance with the agreement known as the Joint Comprehensive Plan of Action, or JCPOA.
The administration said the lifting of sanctions on the three former officials and two companies is unrelated to the indirect discussions in Vienna that are to resume this weekend.
"There is no linkage, there is no connection to the de-listings that we announced today to the JCPOA or to negotiations that are ongoing in Vienna," State Department spokesman Ned Price told reporters. However, he was unable to offer a complete explanation of the reasons behind the move, other than it was made in response to a petition for the removals.
"These petitions are reviewed very carefully," he said.
"They are verified by experts to ensure that the information put forward is factual, that it is accurate, and only after we have verified the information put forward in petitions would we undertake a de-listing. In the case of these three individuals it was the result of our ability to verify that there was a change in status or a change in behaviour that allowed us to undertake this de-listing."
Price added that the step demonstrates "our commitment to lifting sanctions in the event of a change in status or behaviour by sanctioned persons."
He said that practice is "consistent with good sanctions hygiene and administrative processes." Still, he could not say what the "change in status" or "change in behaviour" had been, and Iran's national oil company, NIOC, and a number of other affiliates remain under US sanctions.
Sanctions have been removed in the past because a target has died, retired or otherwise left their position but there was no indication any of those had happened.
Critics of the nuclear deal and the administration's intent to return to it immediately denounced the lifting of sanctions as a concession in the absence of anything in return from Iran, and while Tehran continues to ignore demands from the U.N. atomic watchdog to explain elements of its nuclear program.
"The Biden administration should not be offering Iran sanctions relief at a time when Tehran is refusing to comply with the International Atomic Energy Agency investigation into its nuclear program," said Andea Stricker, a research fellow at the Foundation for Defense of Democracies.
"Unfortunately, the U.S. just signalled that it is buckling on sanctions relief and the IAEA investigation before a deal is even reached. Iran will be sure to seize on this concession and try to get more."
The sanctions against Ahmad Ghalebani, a managing director of NIOC, two directors of NIOC affiliates and those companies had been imposed in 2013 by the Obama administration.
The 2015 deal with world powers allowed it to sell crude oil again on the international market. President Donald Trump unilaterally withdrew America from the accord in 2018, leading Iran into clandestinely taking its oil abroad and selling it.