While the Copenhagen talks are round the corner, world's biggest greenhouse gas emitters, the U.S and China, have agreed to set targets for reducing the emissions.

Days after the US president Barack Obama said time to secure a legally binding agreement had run out, he and the Chinese president Hu Jintao agreed at a summit that they would continue to press for a comprehensive deal at Copenhagen that would "rally the world".

"Our aim there, in support of what Prime Minister Rasmussen of Denmark is trying to achieve, is not a partial accord or a political declaration, but rather an accord that covers all of the issues in the negotiations and one that has immediate operational effect," Obama said after holding talks with Hu in Beijing.

In a joint communiqué, the leaders said an accord in Denmark should include emission reduction targets for rich nations and a declaration of action plans to ease greenhouse gas emissions in developing countries.

Countering concerns that a non-legal deal could evade many key issues, the communiqué said the climate talks should also increase financial assistance to developing countries, promote technology development, help poor communities to adapt and enhance forest protection.

The two governments also signed agreements to co-operate in the field of low-carbon technology, including the establishment of a joint research centre and the promotion of "cleaner coal" power plants, green buildings and electric cars.

Hu said China and the US had agreed to expand co-operation on climate change, energy and the environment and to "help produce positive outcomes out of the Copenhagen conference".

After weeks in which national leaders have been downplaying expectations for Copenhagen, environmental groups said today's words from the US and China - which between them account for 40% of the world's emissions - had gone some way towards restoring ambitions for the summit. They called for specific targets to be met, but said more political will was needed to ensure a successful outcome.