Scottish Labour has challenged Alex Salmond to set tougher targets for cutting greenhouse gases.

The challenge came at First Minister's Questions where Labour leader Iain Gray accused the SNP leader of "bluster and excuses" on climate change.

Mr Gray said Labour would table an amendment to the Climate Change Bill, increasing Scotland's target for carbon reduction to 40% from 34% by 2020.

The amendment would also direct ministers to seek the advice of the UK's top climate change experts for an action plan for Scotland.

And he challenged Mr Salmond to be "ambitious enough for Scotland" to back this.

The First Minister insisted Scotland already had advice from top experts, including one who said the SNP's plans showed it was possible to deliver "very ambitious" climate change targets.

He said: "This government, this Parliament, led the way on the 80% target while Westminster was still stuck at 60%."

The Holyrood exchanges on Thursday were over the Climate Change Scotland Bill, which sets a greenhouse gas reduction target of 80% for 2050. MSPs will decide whether or not to approve the legislation next week.

The clashes began with Mr Gray saying Holyrood had the power to make the legislation "the most ambitious in the world," and Mr Salmond had promised this.

"The UK target is to reduce carbon emissions by 34% by 2020," Mr Gray went on. "At the moment, the Scottish target is the same.

"Does the First Minister not agree that devolution and our green potential mean we can be more ambitious than that?"

Mr Salmond went on to insist the legislation was "the most ambitious in the world".

"It's true that our interim 2020 target is 34%, as it is in Westminster," he said.

But an implementation plan pointed out that even with the existing powers of Parliament, the figure could reach 36%.

"Of course, if we have more powers - the powers of an independent Parliament - then we could do even more," said Mr Salmond.

Mr Gray said Green campaigner Duncan McLaren, of Friends of the Earth Scotland, had said that the Bill, as drafted, would not lead to targets tougher than the UK`s and was not world-leading.

And Mr McLaren had instead described the UK 2020 target as "world-leading", said Mr Gray.

"Will the First Minister admit that his Climate Change Bill is following, not leading, the United Kingdom, and them maybe we can do something about it?" demanded the Labour leader.

Mr Salmond said Scotland had led the way internationally with the Bill. He said Dr Richard Dixon, of the Stop Climate Chaos coalition, had welcomed commitments on cutting emissions in the energy and transport sectors and had said Scotland was going further than Westminster in these promises.