Klaus Duftschmid, a radioactive waste specialist at the IAEA, told Reuters, "Companies go belly up or labels get worn off...Nobody keeps track of all these sources and this is a problem which has been formally recognised by the U.S."

There had been 2,300 reports of radioactive materials turning up in scrap yards in the United States in 1997, he said by telephone from the U.N. agency's Vienna headquarters.

The United States had particular problems because of the way radioactive materials were licensed to companies. Once a source had been licensed it was no longer tracked.

In the former Soviet Union, weapons sources had been lost or dumped. "This might increase in future because there is more decommissioning going on," he said.

"Weapons and submarines to a large degree will go into the scrap cycle, but hopefully without radiation," Duftschmid added.

Exacerbatimg the problem was the loss of valuable data previously held in Moscow on the location of radioactive sources. That went with the break-up of the Soviet Union.

"In Ukraine they claim 100,000 radioactive sources are unaccounted for," Duftschmid said.

Outside the military sector, radioactive materials could be found in industrial applications such as density gauging levels used by paper mills.

Environmental agencies in Europe relied on scrap yards and steel works to report the discovery of any radioactive metal.

In 1998 the IAEA logged 27 major cases. So far this year four had been brought to its attention, and a fifth case involving alleged plutonium smuggling from Kyrgzstan to the United Arab Emirates was under investigation.

In January, 10 people needed hospital treatment in Turkey after being exposed to radiation from three high-dose cancer therapy units that had been broken up and then sent to a scrap yard.One source is still missing but two have been recovered.

Scrap merchants and stainless steel producers had been installing special detection equipment. "This is the most controlled route because detection systems are not really put up at borders," Duftschmid said.

"Only two countries, Poland and Russia, have extensive monitors on borders."