The U.S. government's Accountability Office says the country faces challenges in securing industrial sites that use radioactive materials which could be used by terrorists.
The GAO says in a new report that investigators visited 33 sites across the country, including those involved in oil and gas production, aerospace, and food sterilization.
The GAO found what it describes as vulnerabilities at a number of the sites. They include open doors, no fencing, and unlocked skylights.
It also found two cases where workers with criminal records, including one who had made terrorist threats, had unimpeded access to radioactive materials.
The GAO says terrorists could use this material to build and set off a so-called "dirty bomb," spreading deadly radioactivity across a populated area.