"Instances of the loss of nuclear materials have been recorded, but what the quantity is another question," Yuri Vishnevsky, head of Gosatomnadzor, or GAN, Russia’s nuclear regulatory agency, said in televised remarks at a news conference.

"Of those situations that we can talk about in actuality, they involve either grams of weapons-grade or kilograms of the usual uranium used in atomic power plants. Most often, these instances are connected with factories preparing fuel — Elektrostal in the Moscow region and Novosibirsk," Vishnevsky said.

Vishenvsky supplied no details on when the thefts occurred and offered no theories on how the material could have been stolen. He also listed no other thefts besides those from the Moscow Region and Novosibirsk Elektrostal facilities, which stopped rather short of the dozens of incidents of nuclear theft in Russia logged by nuclear smuggling databases at Stanford University and the Monterey Institute for International Studies, both of which are regarded as the most comprehensive databases of their type in the world.

According to researchers at the Stanford database, law enforcement officials worldwide have seized 40 kilograms of Russian-origin uranium and plutonium since 1991. Stanford researchers have also estimated that only30 to 40 percent of the nuclear material stolen from facilities in Russia and other territories in the former Soviet Union are ever recovered by authorities.

Vishevsky’s televised remarks, for instance, made no mention of a recent possible plutonium theft from the Volgodonsk Nuclear Power plant, a hotly debated case in which an anonymous US official leaked to the media that this material had been stolen by Chechen separatists. The official also said that other radioactive substances where stolen in that theft — caesium, strontium and low-enriched uranium — which pose a threat to human health if detonated with conventional explosives — a so-called “dirty bomb."

Russian nuclear officials have strenuously denied the US official’s claim.

But there have been other, better-documented thefts that have occurred in the past ten-year timeframe Vishnevsky spoke of. There was, for instance, a 1992 theft of 15 kilograms of highly enriched uranium in the far north Murmansk region when a thief cut through a padlock to an unguarded container holding nuclear submarine fuel.

A spokesman for GAN reached Friday would not discuss any thefts or attempted thefts not mentioned by Vishnevsky.

But added to these thefts — foiled and otherwise — there is currently a group of Russian and international experts scouring arctic Siberia and Russia’s far eastern coast for nuclear batteries powered by strontium-90, which were once used as power sources in these remote areas. These devices — suitable for dirty bombs — were not stolen so much as abandoned or forgotten by the government and search teams, according to interviews with officials at the International Atomic Energy Agency, or IAEA — which helped coordinate the effort — said they weren’t sure whether the teams were looking for 100 or 1000 of these orphaned devices.

Vishnevsky’s remarks on Thursday follow the passage earlier this week by the Federation Council, Russia’s upper house of parliament, of a hefty security bill. But the bill focuses mainly on the country’s security forces and diverts several million roubles that were earmarked for nuclear security. He also spoke critically of a proposed law on technological regulation now being considered by the Duma, the lower house of parliament.

He presented a letter to the Duma, written and signed by a number of prominent scientists, criticizing the proposed law as calling for "the minimal necessary demands for security at the same time that, throughout the whole world and in our country, the demands for security in using atomic energy should be the maximum."

Vishnevsky’s appearance also dovetailed with the release of a report by the Russian American Nuclear Safety Advisory Council, or RANSAC, which is a non-profit organization that advises both the US and Russian Governments on nuclear security issues.

The report offers a less than glowing review of the decade-long Russian-American joint efforts to supply Russia’s fissile materials storage facilities with even rudimentary security. According to rough estimates by US non-proliferation officials, only some 25 to 40 percent of facilities storing fissile materials in Russia have been effectively secured against nuclear thieves.

The IAEA lists two known thefts of uranium from the Elektrostal facility — one in 1994 and 1995, said an agency spokesman. In both cases, the uranium was seized by Russian police. A spokesman for Elektrostal, reached Friday, said he no comment on Vishnevsky’s remarks and would not discuss the details of any of the thefts “for security reasons."

The IAEA also lists the 1994 seizure in Germany of 400 grams of plutonium brought in from Moscow, the Associated Press reported.

A few grams of Uranium-235, which is the most common weapons grade nuclear material, would be insufficient to build a full-scale nuclear bomb. Reactor-grade uranium can be enriched to weapons-grade, but that would require a reactor and the resources one would only be able to find in — and with the complicity of — a sovereign state. But recent US statements against Iraq have led many to believe that Baghdad and a handful of other countries that would possibly pose proliferation risks may possess those resource and capabilities.

Nuclear security concerns have been high since the collapse of the Soviet Union and fears that formerly-state subsidized Russian nuclear scientists would take their knowledge abroad for the right price has been a thorn in the West’s side since 1991. Indeed, Russian nuclear expertise is building the controversial reactor at Bushehr, in Iran, a state US President George Bush has labelled as part of the “axis of evil" — a trio of countries that the United States believes to support terrorism and to be on the market for nuclear weapons-usable materials.

Added to these woes is the near poverty wages paid to guards protecting many Russian nuclear materials storage sites — wages that Russian and Western officials alike fear could induce security personnel to sell nuclear materials to make extra cash.

Local worries are also fanned by rising terrorism, most prominently last months takeover of a Moscow theatre by terrorists, who held hundreds hostage to press their demands that Moscow withdraw troops from Chechnya.

"After September 11th of last year, the situation with regard to security at all Russian nuclear facilities changed for the better, but it still has not reached perfection," Vishnevsky said.

He estimated that bringing security to its ideal level at Russian nuclear operations would require about 6 billion roubles (US$200 million).