Scotland should be allowed to send a minister to the climate change summit in Copenhagen, according to Alex Salmond.
He made the demand in a letter to Prime Minister Gordon Brown which accused Westminster of stalling on the issue.
"It is most regrettable that nine months after making our initial request, we still await a decision," said Mr Salmond.
But as his letter to Mr Brown was on its way, another was coming from the other direction - making an offer that fell short of Mr Salmond's demand.
Energy Secretary Ed Miliband said the Scottish Government could send an official to Copenhagen in December, in line with practice in previous years.
Mr Salmond told the Prime Minister that Holyrood ministers had first raised the matter with Westminster at the end of 2008 but had not yet had a response.
"Scotland has a strong story to tell - as a partner in the UK's efforts to tackle climate change and as a country which now has the most ambitious statutory emissions reduction target for 2020 of any country in the world," said the First Minister.
This would be "a strong signal" for other countries to heed.
"It is therefore appropriate that Scottish ministers be represented on the UK delegation to the UNFCCC (UN framework convention on climate change) conference of parties in December," said Mr Salmond. "In this way, Scotland's example of strong domestic action and close collaboration with partners in the UK and Europe can help to influence the debate at Copenhagen."
The Scottish Government claimed its stance was backed by environment campaign groups.
But Mr Miliband's letter, to Finance Secretary John Swinney, said the Government wanted to give priority to members of the Copenhagen negotiating team and supporting experts.
"However I recognise that your contribution to this international effort is important, so I would be happy to include one of your officials on the UK delegation, which has been an offer made - but not always taken up by the Scottish Government - in previous years," he said.
Inviting Mr Swinney to nominate an official, he said: "The whole delegation will of course be constrained to supporting the UK and EU negotiating line."
He said it was also possible for Scottish ministers to go to Copenhagen with other organisations which had observer status.
A spokesman for Mr Swinney said: "This is an extremely disappointing response to an issue we have been pursuing for nine months, but one way or another Scotland will be represented at the Copenhagen conference.
"The Scottish Parliament has passed world leading climate change legislation, and we have an obligation to make our full contribution to the global challenge we all face, which is why Scotland should be at the centre of this process - not relegated to the fringes by Ed Miliband."
