UNITED NATIONS (AP) - U.N. Secretary-General Ban Ki-moon is calling on member nations to step up the pace of negotiations on climate change.

He says failure to reach a broad agreement before the end of the year would be "morally inexcusable, economically short-sighted and politically unwise."

At a summit at the United Nations, Moon told world leaders they need to "strengthen the ambition" of what is being offered for a deal at Copenhagen, Denmark in December.

During today's conference, much of the attention has been focused on the U.S., which has lagged on climate legislation. President Barack Obama has announced a target of returning to 1990 levels of greenhouse gas emissions by 2020.

Another major greenhouse gas emitter, China, has laid out plans for reducing "by a notable margin" the "intensity" of its carbon pollution.