MONTREAL — Canada has reportedly aligned itself with Russia and Japan to block the extension of the Kyoto Protocol beyond 2012.

U.N. climate chief Christiana Figueres said Friday that Canada is one of three countries among the 36 signatories opposed to extending their emission targets under the pact.

The move by the Harper government has sparked criticism from environmentalists and opposition critics, who argue Canada is now holding back negotiations at a climate change conference in Cancun, Mexico.

The Kyoto Protocol is ineffective because it doesn't include many of the world's largest emitters, including the top two -- China and the United States, Bill Rodgers, a spokesman for Environment Minister John Baird, said on Saturday.

Rodgers said the government remains committed to developing a legally-binding agreement that includes all major emitters.

"We're working as constructively as any country at these negotiations to try to do that," he said.

Steven Guilbeault of the Montreal-based environmental group Equiterre said from Cancun that extending the Kyoto agreement is crucial to countering climate change, especially since last year's summit in Copenhagen drew limited results.

He said "it's no surprise to anybody here" that Canada is opposed to Kyoto, though he said observers were caught off guard on Friday when Figueres told a news conference that Canada was opposed to extending the agreement.

For Guilbeault, the decision is another example of Canada's lack of leadership on environmental issues.

"We used to be a nation that mattered internationally," he said.

Now, he said, Canada's position is, "basically, we'll follow the U.S."

Liberal environment critic Gerard Kennedy, who is also in Cancun, called the move "unacceptable."

He said Canada should be helping to set the agenda, and that it "doesn't make any sense at all that we should be late comers to define what happens."

Bloc Quebecois environment critic Bernard Bigras said the opposition parties should join forces to pressure the Harper government to extend the agreement.

He said the opposition has shown in the past they are capable of solidarity when it comes to climate change.

Earlier this week, Japan said it was pointless to extend the Kyoto Protocol unless China and the United States also accepted binding targets.

The U.S. has rejected Kyoto since it was negotiated 13 years ago, partly because it made no demands on rapidly developing countries like China and India.

Meanwhile, some Latin American countries have said they will not accept the refusal by some developed countries to extend their binding emissions targets, and that doing so will hamper progress on other issues.

Delegates at the 193-nation conference are also discussing setting up a "green fund" to disburse aid to poorer countries to reduce their emissions and adapt to climate change; to make it cheaper for developing nations to obtain climate-friendly proprietary technology; and to finalize more elements of a plan to pay developing countries for protecting their tropical forests.

As the climate talks drag on, the Earth continues to warm. The World Meteorological Organization reported this week that 2010 is on track to become one of the three hottest years, and Canada its warmest year ever.