Canada told the world Wednesday it opposes placing limits on the export of chrysotile asbestos — a "bombshell" expected to derail international efforts to list the mineral as hazardous.

The head of the Canadian delegation at a United Nations summit in Geneva made the statement late Wednesday after a consensus was emerging to label the known carcinogen mined in Quebec as hazardous.

If chrysotile asbestos is listed on Annex III of the United Nations' Rotterdam Convention, "Prior Informed Consent" would be required before countries could export the mineral. After being informed of the hazards, developing countries that import asbestos could refuse to accept the potentially cancer-causing material if they believe they could not handle it safely.

Until Wednesday's declaration, the Canadian delegation had remained silent — fuelling speculation from anti-asbestos campaigners that Canada was letting a handful of other countries do its "dirty work."

The stunning development — confirmed by the UN Environment Program and characterized by the Montreal-based Chrysotile Institute as a "bombshell" — appeared to contradict statements made by Natural Resources Minister Joe Oliver just a day earlier, when he told reporters in Ottawa that the question of Canada's position was "moot" because four other countries — Vietnam, Kazakhstan, Kyrgyzstan and Ukraine — had already spoken up against the listing.

Under convention protocol, unless consensus among countries is achieved, chrysotile asbestos remains off Annex III. The UN meeting ends Friday.

When pressed by reporters about the possibility of a consensus emerging in the face of Canada's silence, Oliver also suggested Tuesday that the federal government would accept the listing. "If they want it to be listed, then it will be listed," he said.

But on Wednesday, India, a major importer of Quebec asbestos, announced it would support the listing after remaining quiet.

As with Canada at past meetings, India either opposed the listing or remained silent, despite a long-standing recommendation of the convention's expert scientific committee that chrysotile asbestos, already banned in many countries, be placed on the list.

Then, Ukraine indicated it could accept the hazardous listing.

Following this development, the head of the Canadian delegation, David Sproule of the Department of Foreign Affairs and International Trade, intervened to pronounce Canada's objection.

Madhu Dutta, an anti-asbestos campaigner from India who is in Geneva to observe the UN proceedings, said Canada's manoeuvre on Wednesday was outrageous.

"Canada was hiding behind the smokescreen of dissenting voices of smaller exporting countries and a 'non-consensus' excuse, but when it sensed that there might be a consensus and chrysotile will be listed, it broke its sinister silence and said no," Dutta told Postmedia News from Geneva.

Guy Versailles, a spokesman for the Chrysotile Institute who is also attending the UN summit, also said it looked like Canada broke its silence only after it appeared a consensus was emerging.

Versailles called Ukraine and its partner, Russia, "heavyweights" at the negotiation table that "could carry the day, but I'm not sure Vietnam could have.

"So when they reversed their position, or were appearing to reverse their position, Canada spoke up," Versailles told Postmedia News.