TBILISI, Georgia (AP) _ Georgian investigators are looking into who was behind of a cache of uranium that was seized by police this week as it was allegedly being smuggled into Turkey, officials said Saturday.

Georgian border officials detained four people on Tuesday for allegedly trying to take the radioactive substance into Turkey, a security official said.

The four, all Georgian citizens, were stopped Monday night at the Sarpi border checkpoint, about 150 miles west of the capital Tbilisi, said Gela Suladze of the State Security Ministry.

They were carrying 2.2 pounds of a radioactive substance believed to be uranium-235, Suladze said.

Since the collapse of the Soviet Union, concerns have been high about nuclear materials possibly being taken from unguarded or poorly monitored facilities in the former Soviet republics and smuggled to other countries.

An investigation into the seizure was underway.