The United States and three key European allies -- Britain, France, and Germany -- say they want to eliminate any confusion about what investment and business deals with Iran are permitted after the nuclear deal.
"We encourage firms to approach our governments to address remaining questions rather than forgo opportunities due to misperceptions or lack of information," the State Department said Thursday.
The U.S. and European Union lifted most sanctions on Iran in January after Teheran agreed to curb its nuclear program.
But some sanctions remain, including those related to human rights and terrorism issues.
Some businesses are still confused over what is and is not permitted and are withholding investment and trade with Iran.
The State Department says it is ready to provide guidance and speedy clarification.
"It is in our interest and the interest of the international community to ensure that the JCPOA [ Joint Comprehensive Plan of Action, the official name of the nuclear deal ] works for all participants, including by delivering benefit to the Iranian people."
The U.S. says this includes the reintroduction of European banks and businesses in Iran.
But President Barack Obama said last month that Iran still has to do more to prove to global firms that it is a safe place in which to do business.
Obama said when Iran tests ballistic missiles painted with slogans calling for the destruction of Israel, businesses get nervous.