Tens of thousands of activists took to the streets of Montreal on Saturday during a worldwide day of protest against global warming.

"In order for politicians to move during these conferences, they have to feel that people are behind them," said Sidney Ribaux of Equiterre.

Quebec Environment Minister Thomas Mulcair, Parti Quebecois Leader Andre Boisclair and Bloc Quebecois Leader Gilles Duceppe were among the politicians who joined the rally.

"I am here today to show the public that we (the government) are with them," said Mulcair, who was among those at the head of the parade.

He said it was "no accident" he was leading the demonstration, following the failure of the province and Ottawa to reach a deal to reduce greenhouse gases that had been expected to be signed at the conference.

"They wanted to be able to submit projects directly with municipalities. That's a non-starter for us here in Quebec," said Mulcair.

Federal Environment Minister Stephane Dion promises there will be an agreement after the election -- if the Liberals again form a government.

"Now we need to improve Kyoto, the next week will be very crucial," said Dion.

Parti Quebecois leader Andre Boisclair pledged that if he becomes premier, he will enact a law to ensure the province meets its six-per-cent greenhouse gas reduction target and will invest in public transport.

The rally in Montreal is expected to be the largest in more than 30 countries, including Japan, Germany, France, Bangladesh, Brazil, Australia and South Africa.

The demonstrations are timed to coincide with the 10-day UN Climate Change Conference that is underway in Montreal until Dec. 9, where delegates from more than 180 countries are to discuss meeting emission targets and what to do in seven years when the Kyoto accord expires.

The summit, with some 10,000 participants, is considered the most important gathering on climate change since 140 nations ratified the Kyoto Protocol in 1997.

That landmark agreement, negotiated in Japan's ancient capital of Kyoto, targets carbon dioxide and five other gases that trap heat in the atmosphere, and are believed to be behind rising global temperatures that many scientists say are disrupting weather patterns.

The treaty calls on industrialized nations to dramatically cut their gas emissions between 2008 and 2012.

The Kyoto accord was delayed by the requirement that countries accounting for 55 per cent of the world's emissions must ratify it. That goal was finally reached, nearly seven years after the pact was negotiated, with Russia's approval last year.

U.S. targeted

As part of the protests, five environmental groups, including Greenpeace and the Climate Crisis Coalition, intend to deliver a petition to the U.S. consulate in Montreal.

The petition has been signed by 600,000 American citizens. It calls on the Bush administration and the U.S. Congress to help put a stop to global warming.

"Listen to these tens of thousands of people," Jennifer Morgan of the World Wildlife Fund's Climate Change Program told The Canadian Press. "The U.S. administration is the biggest obstacle to progress at this meeting. They have come here to (destroy) and slow things down."

In London, protesters passed 10 Downing Street, home of Prime Minister Tony Blair, where they presented a letter demanding that the government reaffirm its support of the Kyoto accord.

Meanwhile, at a protest in Boston, speakers called on Massachusetts to join with seven other Northeast states that are placing restrictions on carbon dioxide emissions from power plants.

The United States, the world's largest emitter of such gases, has refused to ratify the agreement, saying it would harm the U.S. economy and is flawed by the lack of restrictions on emissions by emerging economies such as China and India.

Because of its refusal to ratify the treaty, the U.S. will take no formal part in discussions, but the Americans do have a place at the table because they are participants in the UN Framework Convention on Climate Change, the broader agreement which gave rise to the legally binding protocol.

Observers say the coming days will see delicate negotiations to find a way to bring the United States into talks about future action on global warming, without asking them to commit to firm deadlines.

With a report from CTV's Cindy Sherwin and files from The Canadian Press