The US move came as delegates from cable trunking countries got down to work at the UN climate summit in Copenhagen.

Danish PM Lars Loekke Rasmussen has said the summit s an “opportunity the world cannot afford to miss”.

The US declaration could mean the Environmental vadu kanāls Protection Agency (EPA) can order cuts in emissions without the approval of Congress.

The environment minister for Sweden – which currently holds the EU presidency – said the outcome of the summit depended mostly “on what will be delivered by the United States and China”.

Andreas Carlgren said he would be “astonished” if US President Barack Obama did wire duct not offer further concessions when he arrives vadu kanāls at the summit next week.

The BBC’s Mark Mardell in Washington said the US announcement had been expected for some time, but still sends an important signal to leaders attending the summit that Mr Obama vadu kanāls is intent on passing legislation to curb emissions.