The European Union on Friday gave notice it was not prepared to go beyond a planned 20-percent cut in greenhouse-gas emissions ahead of next month's UN climate talks in Cancun, Mexico.

At the end of a summit in Brussels, EU heads of state and government said making progress on tackling climate change "is becoming ever more urgent."

"It is therefore important that the Cancun Conference deliver a significant intermediate step" towards a comprehensive climate treaty, they said in a statement.

"The European Union," they added, "will reassess the situation after the Cancun Conference including the examination of options to move beyond 20 percent greenhouse gas emission reductions to be prepared to react to the ongoing international climate negotiations."

In 2008, the EU said it would unilaterally cut carbon emissions by 20 percent by 2020, as compared to a benchmark year of 1990.

It also offered to go to 30 percent if other industrialised powers follow suit. The proposal was put on the table, but not reciprocated, at December's world climate talks in Copenhagen.

Since then, the 27-nation bloc has been under pressure from Britain, France and Germany, as well as the European Commission, to deepen to 30 percent.

So far, though, offers from other major industrialised countries are still below the 20-percent mark and critics say that further carbon curbs will hit Europe's fragile economies.

The Brussels summit also reiterated its support for a second commitment period under the Kyoto Protocol, whose pledges expire at the end of 2012, "provided the conditions... are met."

The November 29-December 10 talks in Cancun take place under the flag of the UN Framework Convention on Climate Change (UNFCCC).

The meeting takes place a year after a chaotic summit in the Danish capital on rolling back the threat of climate change after 2012 and channelling aid to poor countries at risk from rising seas, storms, drought and flood.

Cancun will at best deliver progress in areas such as short-term financial aid, preserving tropical forestry and encouraging the transfer of cleaner technology to poor countries, say experts.

But a full-fledged post-2012 treaty will have to wait for further negotiations, possibly concluding in South Africa at the end of 2011, they say.