"We estimate that there are approximately 40 institutes that were part of the Soviet biological weapons program. These institutes often contain extensive collections of dangerous pathogens," said Lisa Bronson, deputy undersecretary of defense for technology security policy and counterproliferation.
"They face threats from within -- (such as) underemployed experts -- and from without -- (including) poorly secured facilities and weak inventory controls," she told the Senate Armed Services Committee's Subcommittee on Emerging Threats and Capabilities.
Bronson noted that Russia presents "unique challenges."
"We continue to be concerned with Russia's compliance with the Biological Weapons Convention.
"Keeping Russia's bioweapons technology, pathogen collections and expertise out of terrorist hands strengthens US national security," she said.
"However, those national security benefits need to be carefully weighed against the inherent risks of engagement. The risk of misuse can never be reduced to zero, but we are using policy and implementation strategies to minimize this risk and allow us to focus on the goal of biological weapons proliferation prevention."
In a speech at the National Defense University last month, President George W. Bush declared "the greatest threat before humanity today is the possibility of secret and sudden attack with chemical or biological or radiological or nuclear weapons."
"America, and the entire civilized world, will face this threat for decades to come," Bush said, adding: "We must confront the danger with open eyes, and unbending purpose."