"I really am confident that at the end of the day, the deal will be struck," Yvo de Boer said in a speech at the Paris-based Organisation for Economic Cooperation and Development.

His comments came a day after the European Union and environmentalists at U.N.-led talks in Bonn called for action on climate change but were met by reluctance from the United States, which said it was too early for substantial steps.

The Copenhagen meeting at the end of next year is intended to agree a new treaty on reducing greenhouse gas emissions that would come into force after the first round of the Kyoto Protocol expires in 2012.

De Boer said growing public awareness of the cost of failure to take action on global warming would push governments into taking action, particularly after the agreement reached at the Bali summit on climate change last year.

"I think that the world is expecting an agreed outcome in Copenhagen," he said. "Just as no self-respecting politician could leave the conference in Bali without negotiations being launched, I believe that no self respecting politician can leave Copenhagen without the deal having been concluded."

He said the new pact should be tight and focused and should leave national governments as free as possible to shape and implement their own policies.

"For the Copenhagen agreement to be really successful, it should be as short as possible and focus on the main issues that you can only make effective through an international agreement," he said. "I hope that not all kinds of stuff will be loaded on that doesn't really belong in that agreement."

Speaking to reporters earlier, De Boer said that concrete action from the United States had been hindered by the presidential election but he believed that all main candidates in the race had shown real awareness of the need for action.

He refused to criticise the U.S. stance, saying Washington had acted responsibly in declining to lay down commitments that would concern a future administration. He said he hoped for an advance next year.