A White House official says the United States will announce a target for reducing greenhouse gas emissions before the international conference on climate change at Copenhagen in December.
The target is expected to be in line with figures contained in legislation before the US Senate - a reduction of about 17% to 20% from 2005 levels by 2020, the BBC reports.
The absence of a US target has widely been seen as the single biggest obstacle to agreement at the United Nations summit, which aims to reach a new international accord to fight global warming, the BBC reports.
At the weekend, the Danish hosts announced more than 60 heads of state and government had pledged to take part in the two-week negotiating session.
The official indicated that US President Barack Obama would join them if it appeared his presence would increase chances of the 192 parties reaching agreement.
The Copenhagen summit is no longer expected to result in a binding treaty to replace the 1997 Kyoto Protocol. However, observers say the fact so many world leaders are attending will raise expectations there is the political will to make emissions cuts.
Meanwhile, the UN World Meteorological Organisation says concentrations of greenhouse gases - the major cause of global warming - are at the highest levels ever recorded and are still climbing.
Head of the agency Michel Jarraud says the trend could be pushing the world towards the most pessimistic assessments of the rise in temperatures expected in coming decades and this underlines the need for urgent action, Reuters reports.
Presenting the agency's annual Greenhouse Gas Bulletin, Mr Jarraud says carbon dioxide is entering the atmosphere at an accelerating rate.
