Industrialised countries must deliver immediately on their promised pledge of USD 30 billion towards climate finance to assist poorest countries to adapt to global warming, failing which the upcoming UN climate meet meeting in Mexico would lack "credibility", the UN said on Wednesday.

The Conference of Parties of the United Nations Framework Convention on Climate Change (UNFCCC) will meet in Cancun in November to hammer out a legally-binding climate change agreement that failed to materialise during the Copenhagen meeting of world leaders last year.

So far, the industrialised countries have not delivered on any of their Copenhagen promises, especially in the realm of climate finance.

"The credibility of the industrialised countries who had promised USD 30 billion as short-term finance to assist the poor countries during the Copenhagen meeting last year will be tested at the upcoming Cancun meeting of the Conference of the Parties of the UNFCCC," said a senior UN official, who preferred anonymity.

"If there is no immediate provision of new funds for short-term climate finance of USD 30 billion at Cancun, the meeting will have no credibility," the official said, suggesting that it is important that the industrialised countries live up to their Copenhagen pledge.

The official also conceded that the Cancun meeting will only help re-start the climate change negotiations in fully earnest, suggesting that there would not be any legally-binding climate change agreement at the Mexican city.

Climate finance is described as the "golden key" for arriving at a legally-binding climate change agreement and it was conceived in Copenhagen to address the mitigation and adaptation commitments for the poorest countries.

There are three vital components to climate finance.

First, the industrialised countries would provide short-term funds to the tune of USD 30 billion through a fast track mechanism during 2010-2012 to assist the poorest and most vulnerable nations for undertaking adaptation measures.

Second, the industrialised countries committed to provide USD 100 billion per year by 2020.

And third, the rich countries agreed to establish a clean energy fund- the Copenhagen Green Climate Fund.

Until now, the industrialised countries have not released any significant amount of funds towards short-term climate fund of USD 30 billion.

Though some Nordic countries in Europe offered some immediate funds, the major industrialized countries have remained silent till now, the UN official said.

Meanwhile, the UN Environment Programme has stepped up its efforts to accelerate action on climate change suggesting to nations that if they combine substantial cuts of carbon dioxide emissions alongside accelerate moves across a suite of other green house gases and pollutants.

"It is clear that the world must deploy all available means to combat climate change," said Achim Steiner, the executive director of the UNEP.