The United Nations climate change conference entered the high-level stage on Tuesday in Cancun, a resort city on Mexico's Caribbean coast, with disputes over the extension of the Kyoto Protocol beyond 2012 still unresolved.

UN Secretary-General Ban Ki-Moon and Mexican President Felipe Calderon are among the officials that spoke at the opening ceremony of the upgraded portion of the annual talks, which aims to find a solution to fight global warming.

"We do not need to find solutions to all problems, but we need to make progress on all aspects," Ban told the ceremony, citing progress on mitigation and national emissions reduction commitments.

The secretary general called on parties to agree to a modest deal in Cancun without holding out for perfection.

"We cannot have a perfect agreement at this time ... perfect is the enemy of good," he said.

In Cancun, "every country can and must do more," Ban said. " Business as usual cannot be tolerated. Cancun must represent a breakthrough."

Ban also expressed his deep concern that the international community's efforts on climate negotiations so far have been insufficient.

"The pace of human-induced climate change is accelerating. We need results now, results that curb global greenhouse emissions," the UN chief said. "Nature will not wait while we negotiate. Science warns that the window of opportunity to prevent uncontrolled climate change will soon close."

Little progress was made during the first week of the UN conference. Developed countries, particularly Japan, and developing countries remain sharply divided over whether to extend the Kyoto Protocol.

Japan opposed to committing to a new period of the Protocol, while Venezuela, Ecuador and Bolivia have said they will not sign any other accords unless developed nations sign on for a new period.

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.