WASHINGTON, July 18 (UPI) -- The last of the highly enriched uranium stored in Bulgaria was removed from the country Thursday and transported to a secured site in Russia.

Officials from the U.S. National Nuclear Security Administration, responsible for the operation, say almost 14 pounds of spent nuclear fuel left over from the Soviet era has been transported out of Bulgaria, the NNSA reported.

The removal of the uranium, stored in Bulgaria since the 1970s, is part of an initiative to deter nuclear proliferation by terrorist groups and other militants whose stated goals include detonating a dirty bomb constructed with nuclear material.

"The complete removal of all highly enriched uranium from Bulgaria is another milestone in NNSA's cooperative effort to reduce the threat of nuclear proliferation and prevent nuclear terrorism," Thomas D'Agostino, NNSA administrator, said in a statement.

"Bulgaria's commitment to remove and secure dangerous nuclear and radiological material at civilian nuclear sites demonstrates the international commitment to non-proliferation and global threat reduction."