Ukrainian police have seized nearly 375 pounds of highly radioactive cesium-137: Ukraine Police Seize Radioactive Material.

In a joint action, Ukraine’s police and state security agents seized two containers of cesium-137 and arrested three men from the southern city of Simferopol on the Crimean peninsula, police spokesman Yuriy Kondratyev told The Associated Press. An unspecified number of people were detained throughout Ukraine.

Cesium-137 is considered a likely ingredient for a so-called “dirty bomb,” in which conventional explosives are combined with radioactive material.

Cesium-137, a highly radioactive material, is used in soil-testing gauges in construction and is found in photoelectric batteries and vacuum valves. It explodes if it comes into contact with water, and exposure to it can cause blood diseases, sterility and birth defects.

Police and state security agents acted on a tip-off that two buyers from the Ukrainian capital, Kiev, were ready to purchase cesium at an estimated price of $60,000 per container, Kondratyev said. Each container seized weighed more than 187 pounds, he said.