The Obama administration is accusing the Iranian government of entering into a "secret deal" with al-Qaeda
to funnel money and insurgents from the Middle East to Afghanistan and Pakistan.
The Treasury said Iran has allowed al-Qaeda operatives to build a "core pipeline" to funnel cash and extremists to the front lines.
It said Iran had become a "critical transit point" for money and recruits, and slapped sanctions on six alleged al-Qaeda agents. They include an Iran-based member allegedly operating with the permission of authorities in Tehran.
The sanctions freeze any assets the six may have in the US and ban Americans from commercial or financial transactions with them.
The Treasury said its exposure of the deal and the sanctions would further set back Iran and al-Qaeda's extremist agenda.
The US Treasury named Iran-based Ezedine Abdel Aziz Khalil, also known as Yasin al-Sura, as a "senior al-Qaeda facilitator" who has operated from inside Iran since 2005 "under an agreement between al-Qaeda and the Iranian government."
Khalil moves al-Qaeda money and recruits from across the Middle East through Iran and then to Pakistan "for the benefit of al-Qaeda senior leaders," Washington said in a statement.
Pakistan-based Atiyah Abd al-Rahman, formerly al-Qaeda founder Osama bin Laden's "emissary in Iran," according to DC, was also named on the list. Rahman is currently al-Qaeda's overall commander in Pakistan's tribal areas, it said.
Four other men – Umid Muhammadi, Salim Hasan Khalifa Rashid al-Kuwari, Abdallah Ghanim Mafuz Muslim al-Khawar, and Ali Hasan Ali al-Ajmi – were also named as part the operation working through and in Iran.
"This network serves as the core pipeline through which al-Qaeda moves money, facilitators and operatives from across the Middle East to South Asia," the Treasury said.
The Treasury did not say where Muhammadi is based, but Kuwari and Khawar are believed to be based in Qatar, while Ajmi is based in Kuwait.
The sanctions mean the American people and businesses are forbidden to engage in commercial of financial transactions with any of the men, and that any of their assets in the United States are frozen.
The announcement was made despite disagreements in the US intelligence community about the extent of direct links between the Iranian government and al-Qaeda, officials said. Most analysts agree that the relationship between the two is murky, at best.
AP and AFP contributed to this report