Yvo de Boer, executive secretary of the UN Framework Convention on Climate Change (UNFCCC), said the announcement on Monday by Japanese Prime Minister Yasuo Fukuda, was useful but sketchy.

"I see it very much as an offer that is being put on the table towards the international negotiations, in the same way that Europe has put an offer on the table," de Boer told reporters at climate talks in Bonn.

But, he said, "it doesn't go far enough."

Fukuda called for cuts of 60 to 80 percent in Japanese carbon emissions by 2050, but did not make any pledge as to the medium term, which is a major factor in the global-warming debate.

He referred to a government report which said Japan could reduce emissions 14 percent by 2020 from the level in 2005, but he did not commit to it.

The European Union has committed to a 20-percent cut in carbon emissions by 2020 from 1990 levels.

It has offered to deepen this to 30 percent if other major economies follow suit.

De Boer, speaking to reporters on the sidelines of UNFCCC climate talks in Bonn, said it was "hard to say" whether a Japanese 2020 reduction target of 14 percent -- if it came to be enshrined as a government goal -- would be comparable to the EU's 20 percent.

"If this becomes a formal Japanese government position, then it will be playing ball, then it will be Japan putting a counter-offer on the table," said de Boer.

"Then the important thing will be to sit down and look at the (comparable) effort... Japan has a very efficient economy, so in that sense, for Japan to have a smaller numerical reduction figure than the European Union, (this) could still lead to the same effort."

The EU has also proposed a cut of 60-80 percent by 2050, compared with levels in 1990.

But the EU proposal is more ambitious than Japan's announcement, which uses 2005 as a base year. Japan's emissions rose by 6.9 percent between 1990 and 2005, according to UNFCCC figures.

The 11-day talks among senior officials in Bonn, due to wrap on Friday, are a step in the marathon "Bali Roadmap" for concluding a new global pact on greenhouse gases by 2009.

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