Russias domestic intelligence agency has detained five people suspected of trying to smuggle a dangerous radioactive isotope out of Russia, claiming the group planned to incriminate Moscow in a false-flag attack on Ukraine, state media reported Friday.The Federal Security Service (FSB) said the five unnamed individuals acting in coordination with a Ukrainian citizen were caught illegally purchasing 1 kilogram of Cesium-137 for $3.5 million in the interests of a foreign customer.Exposure to Cesium-137 which is commonly used in mining operations can cause serious illness and even death.The purpose for smuggling the radioactive substance from Russia abroad [was to] use it against Russian interests during the special military operation, the FSB said, using the Kremlins preferred term for its invasion of Ukraine.Law enforcement officials claimed the five individuals had sought to conduct a propaganda campaign" by staging a false-flag operation with "weapons of mass destruction.It was not possible to independently verify the claims.Video released by the FSBs press serviceshowed surveillance footage of several men carrying a metal safe from an auto repair shop into a vehicle, after which they were detained by masked FSB agents.One of the detainees shown in the video identified himself as a citizen of Russia, Ukraine and the self-proclaimed Donetsk peoples republic.Russias Interior Ministry has initiated criminal cases into the misuse of and preparations to smuggle nuclear and radioactive materials over the incident.