President Yeltsin's former environmental safety adviser yesterday revived fears that suitcase-sized nuclear weapons - each capable of killing up to 100,000 people - have disappeared and may now be in the hands of terrorists.
In a letter to the Moscow newspaper, Novaya Gazeta, Prof Alexei Yablokov, a member of Russia's Academy of Science who was sacked by Mr Yeltsin in April, said the allegation that up to 100 portable nuclear bombs were missing was "definitely not groundless".
Gen Alexander Lebed, the former head of President Yeltsin's security council, first raised the prospect of loose Russian nuclear weapons in an interview with a US television network broadcast 10 days ago.
But the Russian government said all the military's nuclear weapons were accounted for and accused Gen Lebed of seeking cheap publicity to boost his flagging presidential ambitions.
The Clinton administration also discounted his claims.
However, Prof Yablokov gives new authority to Gen Lebed's allegations because he says the weapons were controlled not by the Russian military but by the KGB, which developed them in the 1970s for "terrorist purposes".
"These nuclear charges were not registered by the defence ministry and as a result could have been dropped from the list of nuclear devices under international disarmament negotiations," the professor claims in his letter.
So both Gen Lebed and the defence minister could be right; the Russian army and navy might have all their nuclear missiles present and correct but the KGB bombs could be missing.
There are proven cases of missile components being smuggled out of Russia but not a whole nuclear bomb.
Earlier this month, the Centre for Policy Studies, a Moscow-based think tank, concluded that 30 gyroscopes needed to build long-range nuclear missiles had found their way to Iraq from a Russian missile dismantling base. They were discovered in Iraq by UN inspectors.
Prof Yablokov worked in the government from 1989 until this year and is a widely respected environmentalist.
His knowledge of military affairs will be questioned, though, and debate will now focus on whether there ever was a KGB nuclear bomb.