The FBI (search) warned law enforcement agencies of the potential for floating explosive devices — otherwise known as terrorist improvised mines — according to the weekly bulletin issued by the agency and obtained by FOX News.

"Although large-scale, military-style mining operations against the U.S. are assessed to be beyond the capabilities of transnational terrorists, the technological sophistication demonstrated in evolving improvised explosive device (IED) construction raises the possibility of limited, geographically dispersed waterborned IED attacks," the FBI said.

"The FBI possesses no information indicating a specific threat involving floating IEDs or terrorist plans for mining US waterways."

"However, international terrorists have shown interest in using floating explosives and the potential for isolated attempts to carry out such attacks cannot be discounted," the FBI said.

The FBI said that there have been some recent incidents involving floating IEDs, but there appeared to be no similarities in how these separate explosives were constructed. The FBI said that the lack of similarities indicates that the floating bombs involved lone individuals instead of a terrorist network at work.

Nevertheless "these incidents demonstrate potential vulnerabilities and the possibility exists that extremists may choose similar tactics to conduct attacks against the U.S. maritime infrastructure.

The FBI then listed possible designs for floating bombs, including IEDs attached to floats or buys, IEDs concealed in floating debris or trashbags and innertubes or rafts carrying IEDs onboard.

The FBI also included a list of potential indicators relating to planning a floating bomb or terrorist mine attacks:

— Reports of launching or retrieving boats from unusually remote areas

— Reports involve aircraft dropping objects at night near harbors, ports or commercial airways

— Reports of abandoned small boats found adrift near sensitive sights

— Reports or incidents of unusual or unidentified floating objects near vessels or in harbors, ports or commercial waterways

— Evidence suggesting trends or patterns in terrorist-related hoaxes or threat reporting dealing with mines or floating IEDds

— Reports of suspicious requests for hydrographic charts associated with naval or commercial port facilities

— Reports of attempts to purchase or steal large magnets, large styrofoam blocks, large diameter PVC pipe, empty compressed gas cylinders or watertight storage drums.

Fox News' Anna Stolley and Catherine Herridge contributed to this report.