Dozens of experts - some on horseback - are scouring an area in the west of the former Soviet republic.

The search for the two Strontium 90 generators is expected to last up to two weeks.

Some of the area to be searched is remote and inaccessible, forcing the teams to travel on foot as well as on horseback and by car.

Radiation burns

Around 80 people are taking part in the operation, being co-ordinated by the International Atomic Energy Agency (IAEA).

Most of the team members are from Georgia, but experts from India, France, Turkey and the US are also present, as well as IAEA officials.

The area being searched is 550 square kilometres (200 square miles).

The new search comes four months after two forestry workers suffered severe radiation sickness and burns when they found other Strontium 90 sources abandoned in woodland.

The men are still being treated in France and Russia for the injuries they suffered.

The generators would have been used to power communication stations in remote areas. Six have already been recovered, but two more are still believed to be missing.

The IAEA describes them as "highly radioactive".

The situation in Georgia may just be an indication of the serious safety and security implications orphaned sources may have elsewhere in the world

Abel Gonzalez IAEA spokesman

More than 280 other radioactive sources have already been recovered from Georgia since the mid-1990s. Some were from abandoned Soviet military bases.

The IAEA has been working with the Georgian authorities since 1997 to try to recover missing material, and to upgrade safety, but officials say it is not the only country where abandoned, or "orphaned", radioactive sources could present a major hazard.

"The situation in Georgia may just be an indication of the serious safety and security implications orphaned sources may have elsewhere in the world," said Abel Gonzalez, the agency's director of radiation and waste safety.

"The IAEA's work in Georgia is part of a comprehensive plan that includes Agency assistance to States to help them regain control of such orphan sources."

A second phase of the operation will involve carrying out an aerial and road survey in September, with the eventual aim of finding other material still at large.