Ministers from around the world have been urged to work through the night to make the "crucial choices" needed to secure a new deal on climate change.
United Nations talks in Paris are entering penultimate day of official negotiations, with efforts to break divisions on key issues in the agreement which aims to avoid dangerous climate change and provide finance for poor countries to deal with the impacts of global warming.
The latest draft of the text contained the potential for ambitious targets on curbing rising global temperatures and cutting emissions over the coming decades, as well as weaker options.
But concerns have been raised that there were not clear enough measures to achieve emissions cuts, with calls for a more robust "review and ratchet" mechanism that would see countries re-examining and raising their level of pledged climate action if appropriate every five years.
A new version of the text is expected later today, after French foreign minister Laurent Fabius, who is chairing the talks, urged ministers to work through the night to achieve a new draft.
Amid diplomatic wrangling, a "high ambition coalition" of more than 100 countries has emerged, calling for a strong deal at the negotiations by 195 countries.
The coalition, which includes the European Union, Norway, some of the poorest countries in the world, the US and nations including Mexico and Colombia, has warned it would not accept a minimalist or bare bones agreement.
One of the key things the coalition wants is the five-year review and ratchet mechanism.
Making sure ambition can be raised is key to achieving a 2C limit to global temperature rises - beyond which "dangerous" climate change is expected - or the more stringent 1.5C many countries have backed.
This is because the current pledges by countries for climate action they will take up to 2030 will only put the world on a path to almost 3C.
The issue of "differentiation" - the difference between the responsibilities and action of different countries - also remains a thorny issue in the discussions.
Some countries, thought to include China and India, are trying to maintain the UN climate convention's original strict split between developed and developing countries laid down in 1992, while others such as Europe are seeking wording that reflects the range of countries' development and their ability to act.