The National Biodefence Analysis and Countermeasures Centre (NBACC), due to be completed in 2008, will house heavily guarded and hermetically sealed chambers in which scientists simulate potential terrorist attacks.

To do so, the centre will have to produce and stockpile the world's most lethal bacteria and viruses, which is forbidden by the 1972 Biological and Toxin Weapons Convention. Three years before that treaty was agreed, President Richard Nixon halted the production of US biological weapons at Fort Detrick in Maryland. The same military base is the site for the new $128m (£70m), 160,000 sq ft laboratory.

The green light for its construction was given after the September 11 attacks, which coincided with a series of still-unsolved anthrax incidents that killed five people. The department of homeland security, which will run the centre, says its work is necessary to protect the country. "All the programmes we do are defensive in nature," Maureen McCarthy, director of homeland security research and development, told the Washington Post. "Our job is to ensure that the civilian population of the country is protected, and that we know what the threats are."

The biological weapons convention stipulates that the signatories must not "develop, produce, stockpile, or otherwise acquire or retain" biological weapons, and does not distinguish between offensive and defensive intentions.

A presentation given by Lieutenant Colonel George Korch said the NBACC would be used to apply "red team operational scenarios and capabilities" - military jargon for simulating enemy attacks.

Some analysts say the extraordinary secrecy surrounding the project will heighten suspicions of US intentions and accelerate work on similar facilities around the world.

Guardian Unlimited © Guardian Newspapers Limited 2006

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