"The Secretary-General is exploring ways and means ... to facilitate global efforts for dealing with climate change," de Boer told Reuters by telephone after flying back to Europe.

Ban's envoys would "explore the possibility of a high-level meeting ... possibly on the margins of the UN General Assembly" in New York in September, de Boer said.

"It doesn't necessarily have to be heads of state," he added. "It could be a different level, such as foreign affairs or energy ministers."

On March 1, Ban said global warming posed a threat as great as war and urged the United States to play a leading role in combating climate change. But Ban's spokeswoman said at the time that there were no plans to arrange a summit despite pleas from UN environment agencies.

"I don't think it's a change of heart. What's being explored is ... a high-level meeting to engage a broader constituency -- foreign affairs, energy, trade, economy, transport," de Boer said.

"It needs a broader push and broader support," irrespective of whether leaders meet, he said. World talks on expanding a fight against global warming, widely blamed on burning fossil fuels, are stalled.

RISING SEAS

UN scientific reports this year say that mankind's emissions of greenhouse gas are "very likely" to be causing global warming that could bring more hunger, droughts, floods, heatwaves, melt glaciers and raise sea levels.

De Boer says the world needs to speed up talks on widening the UN Kyoto Protocol, which sets cuts on emissions by 35 industrialised nations until 2012. The United States and Australia pulled out in 2001, reckoning Kyoto too costly.

Kyoto nations make up only about a third of world emissions of carbon dioxide, the main greenhouse gas. Only Russia is bound to a Kyoto target of the top four emitters -- the United States, China, Russia and India.

De Boer said that a new meeting could build on, rather than duplicate, a Group of Eight summit in June at which German Chancellor Angela Merkel wants to focus on climate change.

The G8 summit will be joined by heads of China, India, Brazil, Mexico and South Africa. Together the G8 and the five make up the bulk of world emissions of carbon dioxide.

De Boer said that the G8 summit omits groups such as small island states, threatened by rising seas, the poorest nations such as in sub-Saharan Africa, and Australia.