OSLO: The United Nations urged governments on Monday to make deeper cuts in greenhouse gas emissions quickly, saying the world will otherwise overshoot a ceiling for global warming agreed this month in Mexico.

The UN Climate Change Secretariat also called on countries to work out the details of new institutions, such as a " Green Climate Fund" to help poor nations, agreed on Dec. 11 at the 190-nation talks.

"All countries, but particularly industrialised nations, need to deepen their emission reduction efforts and to do so quickly," Christiana Figueres, head of the Secretariat, said in a statement.

She said existing pledges for curbs on greenhouse gas emissions were only 60% of those needed to limit a rise in temperatures to below 2 degrees Celsius (3.6 Fahrenheit), the level agreed in Mexico to avert dangerous change.

The Mexico talks asked nations formally to list their emissions curbs, many of them already made under a non-binding accord in 2009 at a summit in Copenhagen.

It asked for ideas about how listings could be done by March 28, 2011, but set no firm deadline for completion. A problem is that many countries have unclear strings attached to their national pledges for fighting global warming.

Japan is offering a 25% reduction in emissions from 1990 levels by 2020, for instance, as part of a future deal involving what it says must be "ambitious" targets by all major economies such as China or India.

And Washington has promised cuts in US emissions of 3-4% below 1990 levels by 2020, in line with anticipated US legislation. That is not possible after gains by Republicans, who are sceptical of tougher action, in mid-term elections.

The talks in Cancun helped put UN negotiations back on track after Copenhagen fell short of agreeing a new UN treaty meant to avert more floods, droughts, heatwaves, mudslides or rising ocean levels.

Figueres praised the deal in Cancun but said it "needs to be implemented as fast as possible, and it needs to be accompanied by credible accountability systems that will help in measuring real progress".

In Cancun, governments agreed measures such as a new fund to help oversee $100 billion in annual aid to developing nations from 2020, a new mechanism to slow deforestation and ways to help poor countries adapt to the impacts of climate change.

The agreement widens many of the elements of a non-binding Copenhagen Accord among 140 nations in 2009 into a broader-based UN deal. Bolivia was alone in bitterly criticising the Cancun agreements, saying they were inadequate to slow climate change.