The United States has hit Iran with new sanctions targeting several transport firms it accused of transporting lethal aid from Iran to Yemen and proliferating weapons of mass destruction.
In announcing the measures on December 11, U.S. Secretary of State Mike Pompeo also expressed hope that a weekend prisoner swap with Iran could lead to a dialogue between Washington and Tehran over prisoners.
The Treasury Department slapped sanctions on a shipping network owned by Iranian businessman Abdolhossein Khedri, saying the companies have been used by Iran's Islamic Revolutionary Guards Corps' (IRGC) foreign arm, the Qods Force, to send weapons to Yemen's Shi'ite Huthi rebels.
The Treasury added a layer of new penalties to Mahan Air, which is accused of flying fighters and supplies to Syria to support President Bashar al-Assad.
The department also designated three of the airline's sales offices located in Hong Kong and Dubai.
The moves will subject foreign firms and governments that do business with the targeted entities to sanctions themselves.
In a statement, Treasury Secretary Steven Mnuchin said Iran "uses its aviation and shipping industries to supply its regional terrorist and militant groups with weapons, directly contributing to the devastating humanitarian crises in Syria and Yemen."
Tensions have heightened between Tehran and Washington since President Donald Trump last year withdrew the United States from the 2015 nuclear accord that offered Iran sanctions relief in exchange for curbs on its nuclear program.
Washington has since reimposed crippling sanctions on the Iranian economy, while Tehran has gradually reduced some of its commitments under the deal.
Trump wants to force Iran to renegotiate the agreement, arguing that the terms were not tough enough to prevent Tehran from developing nuclear weapons, agreeing curbs to its ballistic-missile program, and ending its support for "proxy" groups across the Middle East.
Iran has so far refused to do so.
"As long as [Iran's] malign behavior continues, so will our campaign of maximum pressure" against the Islamic republic, Pompeo told reporters in Washington.
The state secretary called the December 7 release of Princeton graduate student Xiyue Wang in exchange for an Iranian jailed in the United States a "happier note" that could yield progress.
"I do hope the exchange that took place will lead to a broader discussion on consular affairs. We are working to use this as an opportunity to continue that effort," Pompeo said.
"I hope that it portends well. We have had some indication that that may be the case," he added, without elaborating.
U.S. officials say Iran is holding one American citizen and five dual U.S.-Iranian nationals.
Iran says U.S. authorities are holding some 20 Iranian nationals in jail, and Foreign Minister Mohammad Javad Zarif on December 9 said Tehran was "fully ready" for more prisoner exchanges with Washington.
Also on December 11, Iranian Foreign Ministry spokesman Abbas Musavi dismissed as "unacceptable interference" in Iran's state matters French President Emmanuel Macron's call for the release of two French nationals jailed in the country since June, according to state news agency IRNA.
Musavi's comments come a day after Macron called for the immediate release of Fariba Adelkhah and Roland Marchal.
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