The United States slapped sanctions on 21 Iranian government firms, boosting pressure over the Islamic republic's nuclear program and alleged support for radical groups including the Taliban.
Accusing Tehran of trying to dodge sanctions by setting up opaque trading companies, the Treasury Department also named a host of banking, mining and other companies --spread throughout Europe and Japan -- as government-backed.
"As its isolation from the international financial and commercial systems increases, the government of Iran will continue efforts to evade sanctions," said Treasury undersecretary Stuart Levey.
Those moves, he said, included "using government-owned entities around the world that are not easily identifiable as Iranian to facilitate transactions in support of their illicit activities."
The Treasury also announced sanctions against individuals and groups to target "the government of Iran's support for terrorism and terrorist organisations," including Hezbollah, Hamas, Islamic Jihad and the Taliban.
Senior members of Iran's elite Revolutionary Guard were among those named, including Mohammad Reza Zahedi and Hossein Musavi -- a commander who, the Treasury said, had "provided financial and material support to the Taliban."
It also accused the Revolutionary Guards of running aid operations in Iraq, Afghanistan and Lebanon as cover for intelligence operations as well as funding militant groups.
The 21 firms included two Belarus-based banks, two Germany-based investment firms, and mining and engineering companies in Japan, Germany, Luxembourg, Italy and Iran.
US citizens and businesses will now be barred from doing business with the proscribed companies.
It is the latest of a series of US moves put pressure on Iran, which Western governments say is trying to build a nuclear weapon.