At least a dozen US-listed companies have been told by securities regulators to disclose business activity in and with Syria, Iran and others deemed “state sponsors’’ of terror by the State Department.

The US Securities and Exchange Commission has written to several companies in the past few months asking why they had not disclosed business dealings in Syria, Iran, Sudan and Cuba. The inquiries are part of SEC reviews of companies’ investment risks to security holders.

Sony, Caterpillar, American Express, Aecom Technology, Iridex and Veolia Environnement are among the companies that received letters from the SEC’s division of corporate finance. Their responses show how sales have shrivelled amid tighter international sanctions and how some companies, such as Sony, have found middlemen in Dubai and other countries to keep limited supply lines open.