The US is further easing sanctions on Iran, making it easier for foreign firms to do business with the country following last year's nuclear deal.
The Treasury Department published new guidance for businesses at the start of the Columbus Day holiday weekend, saying some previously banned dollar transactions with Iran by offshore banking institutions were allowed as long as they did not enter the US financial system.
The clarifications from Treasury's Office of Foreign Assets Control also remove a blanket ban on foreign transactions with Iranian firms that may be controlled by a person who remains subject to US sanctions.
Despite the nuclear agreement, which gave sanctions relief to Iran in return for it curtailing its nuclear programme, the US maintains sanctions on Iran and certain Iranian companies and people.
They are known as "specially designated nationals" or SDNs, for a variety of reasons, including its ballistic missile programme, human rights record and support for groups the US deems to be terrorist organisations.
The new treasury language says foreign transactions with non-sanctioned entities that are nonetheless "minority owned" or "controlled in whole or in part by an Iranian or Iran-related person on the SDN list" are "not necessarily sanctionable" under US regulations.
Friday's steps by the Treasury come amid growing complaints from Iran that it is not getting the sanctions relief it deserves under the nuclear deal because remaining US sanctions have scared foreign companies from doing business in or with the country.
The US insists it has met its obligations and blamed Iranian behaviour for the reluctance of foreign companies do to business in Iran.
At the same time, it has sought to reassure foreign companies that certain transactions with Iran will no longer be subject to US sanctions.