Colombian authorities say they have seized 13.5 kilograms of natural, unprocessed uranium in a sting operation.

Brigadier General Gustavo Matamoros told reporters a man and a woman were arrested in the capital, Bogota, after they offered to sell the uranium to undercover agents for $315 million.

The substance was sent for evaluation to Colombia's Institute of Geological and Mineral Research. El Tiempo newspaper says the institute has concluded the uranium is not a danger to public health.

The U.S. Federal Bureau of Investigation is helping Colombian officials probe where the uranium came from and whether it was meant for terrorism.

The metal, which is mined in South America, is only weakly radioactive in its natural state. It is extremely difficult to enrich uranium for use in nuclear weapons.

Some information for this report was provided by Reuters.