NEW YORK, Nov 12: In the backdrop of the claims made by Osama bin Laden that he has nuclear weapons, the International Atomic Energy Agency (IAEA) officials are not ruling out a possibility of acquisition of nuclear device by terrorists and so called rogue nations.

While President Musharraf and US leaders expressed scepticism over Osama’s claims, US officials say given the vulnerability of material in the former Soviet Union, the increasing professionalism of nuclear smuggling and the relative ease of fabricating a primitive weapon, they cannot rule it out.

Experts and officials are increasingly concerned that terrorists willing to die could create a “dirty bomb”, wrapping more easily stolen radioactive material used in medicine and industry around a conventional explosive, like dynamite, to try to make a significant area of a city uninhabitable for many years.

In a report the New York Times said last year there had been dozens of violations of nuclear security rules in Russia and at least one loss of fissile material. The paper also alleged that Taliban emissaries have tried to recruit Russian scientists and terrorists have tried to stake out a Russian nuclear storage site at least twice.

The Times said officials at the international agencies and Western governments detailed the incidents, citing conversations with Russian officials and verified news reports spoke of such possibilities.

It noted despite significant improvements in Russian nuclear security in the 1990s _ some of it with American money and advice _ up to half of ex-Soviet civilian and military nuclear stockpiles with weapons-grade material are not well protected.

In the Kazakh port of Aktau on the Caspian shore, one ton of plutonium and two tons of highly enriched uranium sit near a now closed breeder reactor.

Ukraine, with 17 nuclear reactors and one research reactor, is considered a country of “serious concern” by officials because of its climate of government corruption and crime.

Russian officials say their fissile nuclear material is under strict and improving controls. But only 10 days ago, in a discussion with officials at the United Nations agency here, Yuri G. Volodin, chief of safeguards for the Russian nuclear regulatory agency, revealed that last year there were dozens of violations of regulations for securing and accounting for nuclear material in his country.

The Russians say they thwarted an effort, at the very end of 1998, by an organized gang to steal 18.5 kilograms of highly enriched uranium from a military weapons facility near Chelyabinsk.

The New York Times said senior officials in Washington do not believe that Osama or even any state interested in a shortcut to a bomb has been able to obtain the roughly 25 kilograms of highly enriched uranium required to make a simple bomb, or the roughly eight kilograms of plutonium, a much more difficult material with which to work.

But they also admit that they cannot possibly know for sure.

The most serious cases, involving large amounts of material, took place in 1993 and 1994 when Russian, German and Czech police officers made large seizures of highly enriched nuclear material manufactured in the former Soviet Union.

In March 1993, in St. Petersburg, nearly three kilograms of 90 per cent enriched uranium-238 were seized; in Aug 1994, in Munich, the police seized about 360 grams of Russian-made plutonium; in Dec 1994, 2.7 kilograms of 80 per cent enriched uranium-235 were seized, part of a shipment that showed up in smaller amounts in other places and which officials hope was not part of an even larger shipment, apparently stolen from Russia.

But in fact the atomic energy agency’s database is only a guide, and perhaps not even a good one. “Are we seeing half the iceberg or only the tip?” said one official, noting that the police consider seizures of drugs, a commodity far easier to secure, to represent only some 10 to 20 percent of what is shipped.