Authorities in Western Europe and the FBI have interrupted four attempts of gangs in Eastern Europe to sell nuclear material to ISIS in the last five years, according to Associated Press.

They have stopped criminals with Russian connections that sought to sell radioactive substances to the Middle Eastern extremists.

The latest case was in February this year, when a smuggler tried to find a buyer from the Islamic State group for a huge cache of deadly cesium, enough to contaminate several city blocks.

Criminal organizations, some with ties to the Russian KGB’s successor agency, are engaged in nuclear materials black market trade in Moldova, investigators say.

Moldovan police and judicial authorities shared investigative case files with the AP trying to spotlight how dangerous the nuclear black market has become.

They say the breakdown in cooperation between Russia and the West means that it has become much harder to know whether smugglers are finding ways to move parts of Russia’s vast store of radioactive materials.