BONN - UN talks have run out of time to meet a December 2012 deadline to put in place a binding successor to the Kyoto Protocol on curbing greenhouse gas emissions, the UN's top climate official said on Monday.

After more than three years of talks, Christiana Figueres said countries could not agree in time a full deal to follow on from Kyoto targets, which bind nearly 40 industrialised nations to emissions cuts in 2008-2012.

Countries would have to ratify any new deal in national parliaments for it to have equal legal force with the Kyoto Protocol.

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That is now considered impossible in the timeframe, given that the earliest a deal could be agreed is in Durban at the end of this year, said Figueres, head of the UN's climate secretariat, speaking on the first day of June 6-17 climate talks in Bonn, Germany.

"Even if they were able to agree on a legal text for a second commitment period (of Kyoto), that requires an amendment to the Kyoto Protocol, it requires legislative ratifications on the part of three-quarters of the parties, so we would assume that there's no time to do that between Durban and the end of 2012," Figueres told reporters.

"Countries have realised this, that they actually stand before the potential of a regulatory gap, and are involved in constructive negotiations as to how they're going to deal with that," she said.

A deal in Durban is widely viewed as unlikely.

The European Union's chief climate negotiator told reporters that 2014 or 2015 was now a more realistic target for a full legal framework.

"Let's say 2014, 2015 is a broadly realistic time, but if parties could agree to do that earlier the EU would be happy to do so," said Artur Runge-Metzger.

He said such a timetable would dovetail with the publication of the next major report by the UN panel of climate scientists in 2014, and a review from 2013-2015 of existing, voluntary commitments.

The UN talks have stalled on the future of the Kyoto Protocol, which only caps the emissions of rich countries. Developing countries want to extend the pact while most developed nations want to replace it.