China Thursday raised the prospects of a climate deal being achieved in Copenhagen by offering to be transparent about its greenhouse gas emission targets.

“We promise to make our actions transparent,” Hu Yafei, a senior Chinese foreign ministry official, told journalists.

His comments, voiced just hours before US President Barack Obama was due to arrive in the Danish capital, were a response to calls by US Secretary of State Hillary Rodham Clinton for “all of the major economies,” and particularly China, to “commit to meaningful mitigation actions and stand behind them in a transparent way.”

Subjecting emission pledges of big polluters to an international Measurement, Reporting and Implementation (MRV) procedure is seen as a key issue in the United Nations talks due to end on Friday.

Hu insisted that any international verification mechanism would have to be done on “a voluntary basis,” and only in a way that would avoid foreign powers intruding on China’s sovereignty.

Clinton, for her part, appeared to have softened her country’s hardline stance on the MRV issue by suggesting that the appropriate verification mechanism was still open to discussion.

“There are many ways to achieve transparency that would be credible and acceptable,” Clinton said.

Lord Nicholas Stern, author of a key report on the economics of climate change, hailed the rapprochement as a potential breakthrough.

“I think they have solved that (row on MRV) through MRT, which is monitoring, reporting and transparency,” he said.

The US and China are the world’s biggest polluters and together account for about 40 percent of all greenhouse gas emissions.

For the Copenhagen talks to produce an effective deal aimed at keeping global warming in check, an agreement between the two is seen as crucial.

China has vowed to curb its emissions growth by reducing its carbon dioxide (CO2) output per unit of Gross Domestic Product (so-called “carbon intensity“).

The US is offering an emission cut of 17 percent against 2005 levels by 2020.

Speaking in Copenhagen, Clinton for the first time publicly endorsed UN calls for rich nations to provide some $100 billion in aid to poor nations most at risk of climate change.

However, Clinton declined to say how much her country would contribute to such a fund and insisted that the US offer hinged on a successful outcome in Copenhagen.

That led to questions from the Group of 77 (G77) poor countries.

“We acknowledge that this is a good signal, but we also acknowledge that it is still insufficient. We need more money, we need to equally ask where is the rest: What about the long-term finance?” G77 leaders asked.

The amount of money that rich nations are prepared to give to developing countries to cope with global warming and reduce their emissions is one of the most contentious issues on the table in Copenhagen.

As some 120 world leaders took turns to address the conference, officials expressed relief that the sides had finally returned to the negotiating table after 36 hours of wrangling over procedural issues.

“I would say: Hold tight and mind the doors, the cable car are moving again,” said UN climate chief Yvo de Boer.

Meanwhile, Danish Prime Minister Lars Lokke Rasmussen confirmed that he had given up on efforts to offer a compromise text aimed at facilitating discussions in the face of objections from the G77.

“After consultations with the G77, China and other groups ... the documentary basis for the work will be the texts reported and presented to the plenary last night,” Rasmussen told delegates.

Rasmussen has come under fire from various quarters, most notably from China, over his handling of the talks.

Late Thursday, leaders from regional groupings such as the European Union and African Union gathered for a mini-summit at the Copenhagen conference centre.

EU leaders called for the summit “to help build a consensus for a global deal that produces an ambitious outcome to this conference,” a statement said.