The message that goes out now is that the world does not care about biological weapons - the most dangerous kind of all

Graham Pearson Biological weapons expert

Donald Mahley said: "In our assessment, the draft protocol would put national security and confidential business information at risk."

The unilateral move is likely to further antagonise Washington's European allies, who have already criticised the US for rejecting initiatives on climate change and the trade in small arms.

The germ warfare agreement aims to introduce measures to enforce the 1972 Biological Weapons Convention by the end of this year.

Unlike other multilateral arms accords, the biological weapons ban currently contains no mechanism to ensure compliance.

While reaffirming its commitment to combating the spread of biological weapons, the US said the measures outlined in the draft would not achieve that goal.

It said it planned to make alternative proposals, but did not specify when.

Iraq was discovered to have developed biological weapons

The draft, which more than 50 other countries had accepted as the basis for further negotiation, would oblige member states to open for inspection sites that could be used for the development of biological weapons.

It also sets out a series of steps for verification, including spot checks.

But the US said the checks would not stop cheating by states wanting to develop biological weapons - and could open the door to industrial espionage.

A number of countries are believed to have developed, or to be developing, the capability to have a biological weapons arsenal.

Rapid developments in the field of genetics only increase the likelihood of proliferation.

The European Union and other major powers backed the Geneva talks, regarding them as a reasonable compromise between the need for an effective inspection system and the desire of many countries to protect legitimate pharmaceutical and biotechnology industries.

Seiichiro Noboru, head of the Japanese delegation to the talks, said the US move had effectively killed off this round of talks.

"Even though I understand some of the rationale, I was rather surprised by the US argument at this stage," he said

Scepticism

Professor Graham Pearson of Bradford University, a retired British government biological weapons expert who had been observing the negotiations, said he feared the US was making a big mistake and would eventually have to reconsider.

"I am really disappointed," he said. "The protocol brought benefits for all. The message that goes out now is that the world does not care about biological weapons - the most dangerous kind of all."

The US had taken a leading role in the push for an agreement on enforcing the 1972 convention since Iraqi armaments discovered after the Gulf War showed that the treaty alone had not stopped countries from developing biological weapons.

But correspondents say the Bush administration's position will fuel suspicions that it is deeply sceptical about the value of a whole range of international accords, whether on arms control or the environment.