Even as envelopes containing anthrax spores are increasing fears of bioterrorism in the United States, a flashpoint looms for the international treaty intended to help prevent such attacks.

A lack of consensus over verification threatens to unravel the 1972 Biological Weapons Convention (BWC) at a meeting next month.

Years of efforts to give the BWC teeth collapsed in July, when the United States vetoed a proposed verification protocol for the treaty (see Nature 412, 365; 2001).

US officials last week confirmed that the 11 September attacks had not shifted their position. Avis Bohlen, assistant secretary of state for arms control, told a United Nations forum that the events had “reinforced our view” that verification was unworkable.

More detailed proposals of verification measures were put forward in Paris last week by US officials at a closed meeting of the Australia Group, an informal alliance of 33 countries that aims to limit the proliferation of dangerous agents and technologies through export controls. But other delegates were unconvinced that the United States can suggest a meaningful alternative to the protocol it rejected in July.

The next of the BWC's five-yearly review meetings is scheduled for next month, and the treaty requires all participants to reach a consensus, however bland, at such meetings. Officials fear that some parties, such as Iran or Cuba, may attack the US verification veto, causing a complete breakdown in the process.

“If you don't get consensus, then you don't have another conference in five years' time, and then the BWC is dead,” says Julian Perry Robinson, a disarmament expert at the University of Sussex, UK.