Appeals from climate campaigners . . .

President George W Bush said last March that the US would not ratify the treaty, although he continues to describe global warming as an urgent problem.

And without Japan's ratification, the protocol stands virtually no chance of entering into force.

Mr Bush said three months ago that its requirements would hurt the US economy, and that it unfairly exempted developing countries from cutting their own greenhouse emissions - arguments challenged by the protocol's supporters.

Talks aimed at finalising the protocol's details and clearing the way for its entry into force collapsed last November in The Hague, amid disagreement between the US and European Union (EU) members.

Main polluters

The talks are due to restart in the German city of Bonn in two weeks' time, with environmental campaigners and many EU governments pressing for ratification despite Mr Bush.

To enter into force, Kyoto must have been ratified by at least 55 of the signatory countries, responsible together for at least 55% of the industrialised world's carbon dioxide (CO2) emissions in 1990.

The US then accounted for 36% of developed countries' CO2. So for the treaty to enter into force without American participation will require the other main polluters, the EU, Japan and Russia, all to ratify it.

But the Washington Post says the Japanese Prime Minister, Junichiro Koizumi, has told Mr Bush that Japan will not ratify the protocol without the US.

Mr Koizumi reportedly said after he met Mr Bush: "Presently, I do not have the intention of proceeding without the co-operation of the US."

First step

Earlier reports had suggested that Mr Koizumi might seek to interest Mr Bush in an amended version of Kyoto, relaxing the targets and timetables agreed by the signatories.

The protocol would require developed countries to cut their emissions of the gases many scientists believe are exacerbating climate change to an average of 5.2% below their 1990 levels.

. . . match increasing flooding in the real world

The scientists regard it as no more than a modest first step, and say the world will need to cut emissions of carbon dioxide by more than half over the next 50 years or so.

So if Mr Koizumi is trying to offer President Bush a more appealing version of Kyoto, he will have an impossibly hard job to persuade many other governments to start renegotiating it from scratch.

Mr Bush's Energy Secretary, Spencer Abraham, told a television station it seemed that Kyoto was not going to be approved.

He said: "The president's approach of pursuing these issues now on a research and technology basis, instead of the completely unfair approach that Kyoto would have forced the US to follow, is the sensible way.

"I'm glad to see Japan joining us in taking that position."

Mr Koizumi is in London for a meeting with the British Prime Minister, Tony Blair, and on 4 July is due to meet President Chirac of France, both of them committed to the protocol's entry into force.