The atomic-energy ministry in Moscow denied knowledge of thefts from nuclear installations, and complained that the accusations were 'perhaps a campaign of provocation'.
But Germany insists that Moscow must face up to the problems on its doorstep. Gunther Beckstein, Bavarian interior minister, said it was certain that the material came from Russia. Bernd Schmidbauer, the German minister with special responsibility for security and intelligence matters, will go to Moscow in the next few days for urgent talks on the danger of smuggled nuclear materials from the east.
Mr Schmidbauer said that potential customers 'have apparently not been successful in getting possession of these substances'. He told the Hamburger Abendblatt: 'There is evidence of supply, but not of demand.' But some German officials have continued to hint that Libya, Iraq or Iran might be interested customers.
Mr Schmidbauer, if only for diplomatic reasons, insisted that Moscow has been co-operating with Bonn. But investigators say they have been stonewalled. Mr Beckstein has complained of 'clumsy diversionary tactics'. An investigator told Focus magazine: 'The Russians have not helped.'
The International Atomic Energy Agency said yesterday that it was 'alarmed' at the high quality of radioactive materials being smuggled out of the former Soviet Union. Last week's seizure, part of a sting operation organised by German investigators, was the largest yet. A Colombian and two Spaniards who arrived on a Lufthansa flight from Moscow were arrested on arrival in Munich - on the same flight as Viktor Sidorenko, deputy minister of atomic energy, who also came briefly under suspicion. They were carrying high-quality plutonium- 239, thought to have come from Russian weapons production.
Last week's seizure was the third in recent months. In May, six grammes of weapons-grade plutonium were found in a businessman's garage in the south-western state of Baden-Wurttemberg. In June, a small amount of enriched uranium-235 was seized in the Bavarian town of Landshut - where the quality, rather than the quantity (less than one gramme), alarmed security experts.
As part of the sting operation, there had been previous meetings with the smugglers in Munich at the end of last month. A small amount of plutonium-239 had already been handed over and 200 grammes of lithium, which is used in producing the hydrogen bomb.
It is unclear who is supplying these materials, though German officials talk of 'under-paid scientists' in Russia. Mr Schmidbauer has suggested that both international crime gangs and Russian officials could be involved. The German Foreign Minister, Klaus Kinkel, has warned: 'Travelling salesmen with nuclear suitcases pose a new atomic danger.'
The scale of the danger - potential, or real - is still unclear. This week's Focus argues: 'The nuclear bazaar of the (German) Federal Republic - that scenario has long become reality.' Bild newspaper wondered: 'Is the smuggling getting out of control?' The Frankfurter Allgemeine Zeitung, in an editorial headlined 'Devil's Stuff', asked: 'Apocalypse now - or later?'