Chechen rebels have claimed responsibility for a container of radioactive cesium found in a Moscow park Thursday night. TIME's Sally Donnelly says that the Russian government is trying to downplay the discovery, though an emergency radiation monitoring system has been activated in Moscow just in case there are other such parcels hidden around the city. The package was not a threat in and of itself. While cesium, which is used in medical research and radiation therapy, is not used in weapons, it could be dangerous if dumped into the water supply or placed in close proximity to an individual. A Russian scientist noted that it could cause cancer if carried around by someone for two weeks. "The government sees this as [Chechen leader Dzhokhar] Dudayev thumbing his nose at Yeltsin by showing that he possesses radioactive materials of some kind," Donnelly reports. "Dudayev has threatened repeatedly to launch a nuclear attack on Moscow. But Yeltsin hasn't said anything, and if he does, we can expect him to say this won't change the government's position at all. There will probably be increased security and surveillance in Moscow, but it won't be too high-profile, so as not to alarm the public." A Russian independent television station broadcast the location of the package, reporting that the station got a tip from Chechen rebel commander Shamil Basayev.