At the end of the first week of the ongoing UN climate change conference in the Mexican resort city of Cancun, it seems that the wrestling over the second period of the Kyoto Protocol is heating up.

On late Tuesday, Japan surprised the UN climate talks by saying it won't extend the Kyoto Protocol- the only legally-binding international treaty that commits most of the world's developed countries to making emission cuts. The country inscribed in history for having nurtured the Kyoto Protocol said it will not, under any circumstances, sign up to extend it after the first commitment period expires in 2012.

The strong statement from Japan immediately drew fires from negotiators.

Japan's opposition to extending the Kyoto Protocol is not very constructive, Brazilian Ambassador for Climate Change Sergio Serra told Xinhua on Wednesday.

Its stance on this issue "obviously will" be an obstacle to the Cancun conference "unless Japan compromises a little bit," Serra said.

"There is no way to move forward if we don't have the continuation of the Kyoto Protocol," Serra added.

Su Wei, chief Chinese negotiator and head of the climate change department of China's National Development and Reform Commission, told reporters that he noticed Japan's strong opposition to the second commitment period of the Protocol.

According to Su, Japan's stance has triggered a strong response from negotiators and will greatly affect the balanced outcome of the conference.

Su deemed the Protocol as a key issue to a climate regime and a basis of international framework to address global warming.

"It is one of the crucial issues concerning the success of the Cancun conference," he said.

The Kyoto Protocol was adopted in Japan in 1992 by major emitting countries, which committed themselves to cutting greenhouse gas emissions by 5.2 percent from their 1990 baseline levels by 2012. However, the U.S. Congress has refused to ratify the Protocol.

On Friday, a bloc of Latin American countries issued a stern warning to rich nations that unless they commit to new emissions cuts, the UN climate talks in Cancun will fail.

Negotiators from Venezuela, Bolivia, Nicaragua and Ecuador- all members of the ALBA alliance- said they would not accept the refusal by some developed countries to extend their binding emissions targets under the Kyoto Protocol.

Representing all ALBA nations, Venezuelan negotiator Claudia Salerno said that the bloc would not sign any new agreements unless rich nations commit themselves to a second period in the Kyoto Protocol.

"If there is no second period of Kyoto, it is very difficult that there can be any balanced package" of decisions in Cancun, Salerno said. "We won't sell ourselves."

Meanwhile, the non-governmental organizations Third World Network, Friends of the Earth and the International Forum on Globalization said on Friday that there exists a secret text, which the Mexican government, the COP16 host, would present to the environment ministers.

This document, whose existence was denied by Christiana Figueres, executive secretary of the United Nations Framework Convention on Climate Change, and other delegates, reportedly stipulates the replacement of the Kyoto Protocol with the Copenhagen Accord, which does not include obligatory greenhouse emissions cuts for the signatory nations.

The Chinese negotiator Su told reporters on Saturday that the president of COP16 has told the delegation of each country including China that Mexico will not put forward a secret text.

"As I know, Mexico, the host country of COP16, is always pursuing the principles of 'open, transparent and widening participation' for the climate negotiations this year. I believe Mexico will continue to keep the principles to try to get the results of balance at the Cancun Conference," said Su.

Danish Minister for Energy and Climate Change Lykke Friis also refuted the rumors on Saturday.

"There will always be debates about whether negotiations are being done in a transparent way," Friis said in an interview with Xinhua. "At the creation stage one has to be a deal maker. Anyone who acts as a broker runs the risk of being called non-transparent. But Mexico has done a very good job in creating confidence."