WASHINGTON, Feb 23: Intelligence agencies in Washington have concluded that theft of radioactive materials from Russia's sprawling nuclear complex "has occurred" and the country's atomic power plants remain vulnerable to terrorist attack , according to a new report obtained on Tuesday.

The unpublished analysis by the National Intelligence Council, a CIA-based think tank that serves the entire US intelligence community, came as US President George Bush prepared for a potentially contentious meeting on Thursday with his Russian counterpart, Vladimir Putin.

During their talks in the Slovakian capital of Bratislava, the two leaders are expected to discuss what is seen here as setbacks in the Russian democratic process and non-proliferation, including Moscow's nuclear assistance to Iran and the security of its own nuclear stockpile.

Russian officials have repeatedly denied that Al Qaeda or other terrorist groups could get access to either Russian nuclear weapons or weapons-grade radioactive materials in the hope of fashioning a radiological device known as a "dirty bomb". But in its report to Congress, the council cast doubt on these assurances, arguing that US intelligence experts believe that diversion of nuclear material has already taken place.

"We assess that undetected smuggling has occurred, and we are concerned about the total amount of material that could have been diverted or stolen in the last 13 years," the report said.

The Russian nuclear arsenal is estimated to currently include about 4,000 operational warheads deployed on land- and sea-based intercontinental ballistic missiles and strategic bombers.

Moscow also retains several thousand non-strategic nuclear warheads in storage, plus a network of production and research facilities dealing with fissile substances on a regular basis, according to US officials. -AFP