Negotiators worked into the small hours of Friday at the Caribbean resort beach, trying to narrow differences on how countries will reduce their carbon emissions, with only 20 hours left for agreeing on a balanced package of decisions to battle climate change.

Three working groups on climate fund, transfer of green technologies and the countries' shared vision on long-term goals to curb global warming continued their discussions after midnight.?

Meanwhile, environment ministers from a number of countries were busy with informal meetings and consultations to overcome their differences, and telephone calls between some heads of states and government were also said to be taking place, in a final effort to save the latest round of climate talks.

Developed and developing nations still have major differences on mitigating carbon emissions - how to get countries to act on their pledges to reduce and curb greenhouse gas emissions.

The current negotiations are going on under a two-track system, one of which - the Kyoto Protocol - obliged industrialized countries to cut their carbon emissions. Under the protocol, after it expires in 2012, developed countries are also required to cut emissions between 2013 and 2018.

However, Japan has insisted that it will not renew its commitment after 2012. Russia and Canada have taken a similar position, creating an impasse that is seemingly impossible to break.

"The working group on the Kyoto Protocol has reached a point where there was limited scope for further advancing substantive work until political guidance is given," said John Ashe, the working group chair of the Kyoto Protocol, referring to higher level of orders given by nations' leaders.

As many as 20 world leaders had reportedly contacted Japanese Prime Minister Naoto Kan to call on him to change his position.

"The challenge is that in order to unlock other issues which are almost done you have to unlock this core issue. If that's not resolved, there is no agreement here," said Jennifer Morgan, director of climate and energy program at US-based World Resources Institute.

Jeremy Hobbs, executive director of Oxfam International, called on the European Union (EU) to take firm action to save the Kyoto Protocol.

"We think the EU's leadership is absolutely important in this process," Hobbs said, adding that the EU has a "central role" to play in finding resolutions on the protocol and on climate finance.

"Now it's time for the negotiators to stop blocking and get to work negotiating," he said.

Meanwhile, the United States is refusing to move on establishing a Climate Fund, which is crucial in delivering urgently needed money to protect the most vulnerable, until it get its way on the details of transparency and accountability of emissions cuts in China and other developing economies.