Police spokesman Martin Korch could not say whether the seized material had been enriched to weapons-grade.

"I can confirm that it was uranium-235 and uranium-238," he said.

Slovak and Hungarian officials were to hold a news conference later in the day

Authorities said Wednesday they confiscated the uranium during the arrests of two suspects in eastern Slovakia and a third in Hungary. It remained unclear to whom the suspects were trying to peddle the material.

Uranium is considered enriched if it contains more than 20 percent uranium-235, the fissile form of the element. It is considered weapons-grade if it contains at least 85 percent uranium-235. Natural uranium contains less than 1 percent of the fissile isotope, and uranium-238 is a lower grade form of the element.

The arrests heightened concerns that Eastern Europe could be a source of radioactive material for a so-called "dirty bomb," which would use conventional explosives to scatter radioactive debris.

Slovak and Hungarian police worked together on the case for several months, Korch said. He would not say how long the suspects were under surveillance, or detail how they were arrested and to whom they were trying to sell the material.

Hungary's National Bureau of Investigation had no immediate comment.

Erich Tomas, a spokesman for the Slovak Interior Ministry, and the U.S. Embassy in the capital, Bratislava, said they also had no comment.

The Vienna-based International Atomic Energy Agency, which closely tracks reports of illicit trafficking in radioactive materials, said Thursday it was trying to contact Slovak and Hungarian authorities for more information.

Richard Hoskins, the IAEA official who administers the database, said that last year alone the U.N. nuclear watchdog registered 252 reported cases of radioactive materials that were stolen, missing, smuggled or in the possession of unauthorized individuals — a 385 percent increase since 2002.


Agencies