UN Secretary-General Ban Ki-moon on Tuesday called on negotiators at the climate talks in Copenhagen to complete a legally binding climate treaty "as early as possible in 2010."

"Our goal is to lay the foundation for a legally binding climate treaty as early as possible in 2010," Ban told the opening session of the high level segment of the UN climate change conference.

"The stronger the agreement here in Copenhagen, the sooner it can be transformed into a legally binding treaty," he said.

Many countries are demanding a deal coming out of Copenhagen. But divisions between developed and developing nations over greenhouse gas emission reduction targets and financing were eroding chances of such a deal.

"The time for delay and blame is over," Ban told reporters later.

He said a deadline must be set soon for turning any politically binding agreement reached in Copenhagen into a legally binding treaty. "This deadline cannot be left hanging."

While calling to expedite the negotiating process, the UN chief insisted that the result of the Copenhagen talks should be "strong, robust and substantive."

Ban also praised China's efforts in reducing its emissions. "China has also taken quite important measures by cutting 40 to 45 percent of energy intensity (per GDP unit) by 2020."

He was speaking a day before 110 heads of state and government arrive in Copenhagen for the final stage of the conference, where many of them were expected to expound their positions on how to avoid the worst consequences of global warming.

The UN head called on rich countries to improve their commitments in climate financing for developing nations, saying he was fully aware of particular challenges facing developing countries, especially the poorest ones.

Many developing nations are dissatisfied with rich nations' reluctance to raise their emission cut targets and provide financial support to help them mitigate and adapt to climate change. So far, developed countries have indicated their intentions to give merely 10 billion U.S. dollars annually in the following three years.

An apparent setback came Tuesday when the lead U.S. negotiator said Washington will not commitment to any more carbon emission reductions.

"I'm not anticipating any change" in the commitment that was announced by President Barack Obama a couple of weeks ago, Todd Stern told reporters.

The United States has pledged to reduce its carbon emissions by 17 percent from 2005 levels by 2020, equivalent to a reduction of 4 percent against the 1990 level.

The United States pledged to cut emissions by 7 percent by 2020 against the 1990 level in the Kyoto Protocol. But the country later refused to ratify the document.

The European Union has committed to a reduction of 20 percent from 1990 levels and said it would raise the goal to 30 percent if others, first and foremost the United States, aim higher.

The Copenhagen conference, which was to end Friday, aims for a new global deal on climate change as the first commitment period of the Kyoto Protocol expires in 2012.