The United States, China, India and South Africa have reached a last-minute agreement on climate change, according to a US official in Copenhagen.
No country was “entirely satisfied” with deal but the official called it “a meaningful and historic step forward and a foundation from which to make further progress".
The deal was not enough to combat climate change but was an important first step, the official added.
All eyes have been on the Danish capital as negotiations ran late on the closing day of the two-week UN conference on climate change.
The backing of leading emitter China and other fast developing economies was crucial to any deal.
Details of the reported agreement emerged after a meeting involving US President Barack Obama, Chinese Premier Wen Jiabao, Indian Prime Minister Manmohan Singh and South African President Jacob Zuma.
The conference was scheduled to end earlier on Friday evening and some heads of state, including Russia’s President Dmitri Medvedev and Brazil’s President Luiz Inacio Lula da Silva, left before any sign of a breakthrough.
Last minute push
However Brazil is among the countries to have approved the deal that appeared to bypass other participants at the climate talks.
The accord did not have guaranteed approval from all 193 nations. Noticeably, EU nations were absent from the meeting.
Tensions between China and the United States, the world's two biggest emitters, had been particularly acute after Obama said any deal to cut emissions would be "empty words on a page" unless it was transparent and accountable.
Negotiators struggled all day to find a compromise acceptable to all countries which could avert the threat of dangerous climate change, including floods, droughts, rising sea levels and species extinctions.
A draft text under discussion on Friday included $100 billion in climate aid annually by 2020 for poor countries to combat climate change, and targets to limit warming and halve global greenhouse gas emissions by 2050.
But it abandoned earlier ambitions for any deal in Copenhagen to be turned into a legally binding treaty next year.
swissinfo and agencies
Climate change conference
Nearly 200 countries are meeting in Copenhagen until December 18, trying to reach a global agreement to follow or extend the Kyoto Protocol, which runs out at the end of 2012.
Climate scientists say the world has between 10 and 20 years to reverse the upwards trend in greenhouse gas emissions. If this is not achieved, it will be difficult for humans to adapt to the consequent destabilisation of the climate.
The aim for Copenhagen is to reduce greenhouse gas emissions so that temperatures do not rise globally by more than two degrees in comparison with the pre-industrial age.
The IPCC (Intergovernmental Panel on Climate Change) says industrialised countries need to reduce their emissions by 25 – 40% of their 1990 levels by 2020.
It has called on the rich nations to reduce their greenhouse gas emissions by 80 – 95% by 2050, and developing countries by 50%.
The Swiss government proposes that Switzerland should reduce its emissions by 20% of their 1990 level by 2020.
Switzerland said it is prepared to increase its target to 30%, depending on what happens at Copenhagen.