The move was clearly designed to put increased pressure on Nato at the start of historic negotiations about alliance expansion to the east and a linked Nato-Russia charter.
Ivan Rybkin, the Secretary of Russia's Security Council, told the Rossiiskaya gazeta daily that "in case of a direct challenge our response will be fully-fledged, and we will choose the means - including nuclear weapons".
The announcement was reported as a threat to end Russia's policy of "no first use of nuclear weapons", though many Western observers doubt whether it ever really had such a policy. There had already been indications that the idea, based on a promise by Mikhail Gorbachev, was abandoned in Russia's 1993 military doctrine.
The 1993 doctrine implied that nuclear states or states allied to them might be nuclear targets, whether or not they used nuclear weapons first. Yesterday's statement was clearly directed against neighbouring countries like Poland which, if it joined Nato, would be an ally of nuclear states.
Such a policy makes sense, given the appalling weakness and decomposition of Russia's conventional forces, with low morale and troops unpaid for months. Officers are now failing to turn up for work in order to earn money elsewhere.
In such circumstances, any serious attack on Russia could force the Russians to respond with nuclear weapons which intelligence sources say are still carefully controlled, despite last week's reports to the contrary.
But diplomatic and Nato sources believe yesterday's statement forms part of a classic Russian negotiating technique. At the Madrid summit in July, Nato is likely to issue invitations to some east European countries - including Poland, the Czech Republic and Hungary, to join. The Russians like to take the strategic offensive - establishing an extreme forward position - and then exploit the tactical advantages of the defensive.
Negotiations between Nato's Secretary-General Javier Solana and the Russians started on 20 January. Since then, the Russians have made a series of statements designed to alert the West to their predicament.
On Friday, the Secretary of the Defence Council, Yuri Baturin, and the Defence Minister, Igor Rodionov, said the nuclear forces were in danger of going out of control.
Russia has between 7,000 and 8,000 strategic nuclear weapons and an estimated 2,000 tactical warheads. But the Russians will strive to keep control over these weapons above all others. Western experts dismissed the claims as exaggerated, while admitting that the disintegration of conventional forces could make nuclear first-use more likely.
In fact, nuclear weapons security is still the responsibility of the FSB (heir to the KGB) which receives better pay and conditions than the armed forces. They have a "dual key" arrangement with the strategic missile troops of the armed forces. The threat of nuclear weapons going "out of control" relates to the reliability of staff who keep the weapons working. Nuclear weapons also have a finite shelf-life: some components degrade and therefore have to be replaced - that costs money, which is not available.
Last week's statement was designed to get more money from the Duma - the Russian parliament, whereas yesterday's was a clear shot across the bows of Nato and the main candidates for membership.
Moscow (Reuters) - A strike by hungry workers at a nuclear shipyard in the town of Severodvinsk near the northern port of Arkhangelsk could escalate into a riot unless they are quickly paid long-overdue wages, a local union leader has warned. He said there had been cases of workers fainting from hunger and a number of suicides.