Biological weapons that can wipe out entire populations pose one of the biggest threats to the world today, yet remain almost completely uncontrolled, the British Medical Association said on Monday.

The association urged the United States to end what it called efforts against strengthening the 1972 international Biological and Toxin Weapons Convention when it comes up for renewal in 2006.

"This technology could be used by sub-state terror groups and eventually by deranged individuals," Malcolm Dando, author of the association's study, said at a news conference.

He warned that the development of biological weapons designed to target specific ethnic groups was becoming increasingly possible, and said it was already theoretically possible to re-create devastating viruses such as the Spanish flu epidemic of 1918 that killed as many as 40 million people.

The convention, which banned the development, production, acquisition, stockpiling and retention of germ weapons for offensive purposes, contains no monitoring or enforcement mechanisms. "The best way of describing it is as a gentleman's agreement," said Dando, who is head of peace studies at the University of Bradford.

He said there were strong international mechanisms controlling nuclear and chemical arms, but nothing to control what he termed the "riotous development" of biotechnology.

Dando said the Bush administration had turned its back on many international accords, which he asserted was the key reason the convention remained weak.

The powerful U.S. biotechnology industry has put pressure on the administration not to back strong international monitoring and enforcement mechanisms, arguing that they could stifle research, Dando said.

Russia, which was known to have developed a major biological weapons capability, has also kept a very low profile on the issue, he said. "There are still several of its military laboratories that have not been opened up for inspection. You have to wonder why," he said.

Vivienne Nathanson, head of science and ethics at the British Medical Association, said it was vital for scientists to get involved in self-regulation to ensure that experiments and information not be misused.

"The real key to biosecurity, to not having to deal with deliberately spread epidemics, is to make sure that these materials are not produced," she said. She argued for a code of ethics covering scientists and governments and the enforcement of sensible international laws.