The United States and European powers will work to clear up any confusion companies may have about doing business with Iran following Tehran's acceptance of a deal to curb its nuclear program, the countries said in a statement on Thursday.Despite an influx of investment into Iran from the West, uncertainty over the rules is making some firms reluctant to do business with Tehran. US Secretary of State John Kerry and other US officials have been to at least 18 countries to reassure companies and explain limitations that still exist under US regulations."We will not stand in the way of permitted business activity with Iran, and we will not stand in the way of international firms or financial institutions engaging with Iran as long as they follow all applicable laws," the United States, France, Germany and Britain said in a statement.The statement, released by the US State Department, said the four countries had given companies "extensive guidance on the scope of sanctions lifted and those that remain in place.""Firms may continue to have specific sanctions-related questions or concerns about doing business in Iran, and we stand ready to provide expeditious clarifications," the statement said.Under the Iran nuclear deal, Tehran agreed to curtail its nuclear program in exchange for the European Union and the United States lifting economic and financial sanctions imposed to punish it for its enrichment efforts."It is in our interest and the interest of the international community to ensure the (nuclear deal) works for all participants, including by delivering benefits to the Iranian people," the statement said. "This includes the re-engagement of European banks and businesses in Iran."Since some sanctions were lifted, Iran has agreed to deals worth a total of at least $37 billion with companies including planemaker Airbus, carmaker Peugeot and Italian steel firm Danieli.