"We are making good progress on economic cooperation, but on energy policy and climate change, it is much more difficult," he said.

Diplomats said Washington was refusing to make any firm commitment to reducing greenhouse gas emissions blamed for global warming or to an agreement to curb climate change after the first phase of the Kyoto Protocol expires in 2012.

One said it was possible there would be no agreed joint delcaration at the April 30 Washington summit.

An EU diplomat said no draft text of the declaration on energy and climate change had yet been circulated to EU member states, an unusual delay ahead of such a summit.

German Chancellor Angela Merkel has made the fight against climate change the central priority of her twin presidencies of the EU and the Group of Eight industrialised nations this year and hopes for a breakthrough at a G8 summit in Germany in June.

But US President George W. Bush has stuck to his mainly technology-based approach to reducing pollution.

The US ambassador to the EU, C. Boyden Gray, said in a Reuters interview last week that no US administration would accept binding curbs on emissions as long as China, India and other major emerging countries were not included in the system.

French European Affairs Minister Catherine Colonna said the EU had taken a major step forward this year by committing itself to cut greenhouse gas emissions by at least 20 percent by 2020 compared to 1990 levels and it was time for major partners to make a move.