Federal investigators are probing a major Chinese telecom firm and its U.S. subsidiary for allegedly selling banned U.S. surveillance equipment to Iran, according to a newly disclosed document.

The investigations into ZTE and its Texas subsidiary, ZTE U.S.A., by the FBI and Commerce Department reflect two major U.S. policy concerns — blunting Iran’s appetite for advanced technology that could be used in warfare and understanding the activities of Chinese companies in the United States.

According to an excerpt from an FBI affidavit published on the Web site Smoking Gun, investigators are zeroing in on ZTE’s apparent effort to ship to Iran hardware and software components bought from leading U.S. technology firms despite trade restrictions and embargoes. The affidavit says ZTE attempted to obstruct the investigations.

The Commerce Department has been looking into ZTE since at least March, when it served an administrative subpoena on Dallas-based ZTE U.S.A. for information on monitoring equipment allegedly exported to Iran, according to the affidavit.

Federal law bans the sale, export or re-export of goods, technology or services to Iran. Those who knowingly export goods to Iran are subject to criminal prosecution, and those involved unwittingly face civil penalties.

Justice and Commerce officials declined to comment. Efforts to reach ZTE in Dallas were unsuccessful.

The Commerce Department subpoena followed a Reuters article reporting on ZTE’s sale of powerful electronic surveillance technology to the Telecommunication Co. of Iran, a firm with close ties to the Iranian government, the affidavit said.

Reuters had obtained a “packing list” dated July 2011 that identified products bound for Iran and manufactured by Cisco, Dell, Hewlett-Packard, Microsoft, Oracle and Symantec. The article said the $130.6 million contract between ZTE and the Iranian company was signed in December 2010.

According to the FBI affidavit, agents interviewed ZTE U.S.A.’s general counsel, Ashley Kyle Yablon, in May.

At the time, Yablon told investigators he did not want to be part of a “cover-up” and described efforts by the parent company to conceal the sales to Iran through at least one front company, according to the affidavit.