A U.N. conference working to fix long-term rules to fight global warming beyond 2012 "as soon as possible" was split on Tuesday over whether that meant an accord should be struck in 2008, 2009 or even 2010.

Industrial investors, weighing options ranging from coal-fired power plants to wind energy, are frustrated at the possibility of years of uncertainty about rules for fossil fuel emissions upon which carbon markets depend.

"We need an agreement by 2008," said Hans Verolme, climate director at the WWF environmental group, saying that investors needed time to adapt to new regulations on heat-trapping gases, mainly from burning fossil fuels. "We need action."

"I think it's important to the market that an agreement is reached without delay," said Ron Levi, managing director at energy brokers GFI. Speaking by phone from London, he urged negotiators in Nairobi to reach a deal within 18 months.

The Nairobi Nov. 6-17 climate talks are looking at ways to expand the U.N.'s Kyoto Protocol, which binds 35 industrialised nations to cut greenhouse gases to 5 percent below 1990 levels by 2008-12. Delegates say Nairobi is unlikely to set deadlines.

Last year, ministers at the last U.N. climate talks in Montreal promised to find a Kyoto extension "as soon as possible" with no gap between the first period of Kyoto and a new set of rules starting on Jan. 1, 2013.