"Climate change is the world's greatest environmental challenge," British Prime Minister Tony Blair and French President Jacques Chirac said in a joint declaration issued after talks in London.

"We remain determined to show leadership" on the issue, they said, offering warm support to Russia for having ratified the Kyoto protocol on reducing greenhouse emissions.

They also said they would work toward helping the European Union -- to be headed by Britain in the second half of 2005 -- develop a "medium- and long-term strategy to tackle climate change".

The leaders said their nations would continue to focus on environmental issues in a bilateral working group and commit senior officials to international environmental conferences in the upcoming year.

Chirac was in Britain for an official two-day visit centered on an annual Franco-British summit and the final celebrations of the centenary of the countries' Entente Cordiale alliance.

Blair has said that, in addition to pursuing Middle Eastern peace negotiations, climate change would be a top priority of Britain's presidency both of the G8 and the 25-member European Union.

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