Turkish police detained four men in possession of a nuclear substance in the capital Ankara, broadcaster NTV reported on Monday. The substance was found in their vehicle. A police investigation is underway.

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Californium, a synthetic radioactive element, is produced in laboratories and nuclear reactors and is often used to kick-start a reactor.

The material was meant to be sold for some 70 million dollars, NTV reported, saying about 1.4 kilograms were found in the raid. The story was also reported by the state-run Anadolu news agency.

The source of the material and the identity of its buyer remain unclear. There was no immediate comment from the Ankara Police or the Turkish Atomic Energy Authority when contacted by DPA.

Californium was first synthesized in the United States during the 1950s, and is currently produced in the U.S. and Russia.