The decision takes to 41 the number of products, including several types of asbestos, regarded as a major agent of cancer, which cannot be moved freely across borders under the treaty.

But chrysotile, the most common form of asbestos, was again dropped after producing countries, including Canada and Russia, blocked its inclusion at a preparatory meeting on Saturday.

Decisions under the 1998 treaty - officially the Rotterdam Convention on the Prior Informed Consent (PIC) Procedure - are taken by consensus.

Conservationist group WWF reacted angrily to its exclusion, saying chrysotile, which represents some 94 percent of world consumption, met all the requirements for being listed.

The convention, which has been ratified by over 70 states, allows for global restrictions on any substance which is already the subject of limitations or bans in any two U.N. regions.

In the case of chyrysotile, three regions - represented by Australia, Chile and the European Union - had taken action based on findings the chemical is carcinogenic, WWF noted.

"Canada and Russia's objections to listing chrysotile asbestos are embarrassingly self-interested, protecting domestic exporters interested in selling this dangerous chemical abroad," said Clifton Curtis, director of WWF's Global Toxics Program.