Clashes both diplomatic and violent punctuated the U.N. climate conference in Copenhagen on Wednesday, as major disputes threatened to derail plans for world leaders to sign an agreement that continues to elude negotiators.

While baton-wielding police outside battled protestors in the streets, a series of setbacks and continued roadblocks in negotiations left some of the meeting’s most important nations saying the conference was in trouble.

"The process is not transparent," complained a high-ranking official with the Chinese delegation, one of the conference's most important players. "We are opposed to the proceeding."

The Chinese were referring to the text of a new draft document that was reportedly being circulated by the Danish delegation, which is host to the conference. But there was confusion even on that point, as some denied even the existence of the new text.

SLIDESHOW: Copenhagen Clashes.

With the talks clearly deadlocked, Connie Hedegaard, former Danish climate minister, resigned from the conference presidency to allow her boss, Danish Prime Minister Lars Loekke Rasmussen to preside as world leaders from 115 nations streamed into Copenhagen. She was to continue overseeing the closed-door negotiations.

The Chinese and some other developing nations have objected to what they say is the inclusion of material in the new document that was not covered in negotiations among the many working groups of diplomats who have toiled for more than a week here in the hope of producing an agreement that world leaders could sign. According to the Chinese official, the new document changes seem to have "come from the sky."

Meanwhile, developed countries like the United States and members of the European Union continue to press for verifiable concessions that developing countries say they are unable to make.

In yet another sign of trouble at the conference, the U.S. delegation canceled its daily press briefing, as while some conference attendees scrambled to put a positive face on developments.

"We have made real progress in the last few weeks leading up to Copenhagen and I think it is still possible to reach an agreement here that captures that progress and provides a foundation for achieving even greater progress over the coming years," said Elliot Diringer, from the Pew Center on Global Climate Change.

Diringer called the latest diplomatic snafu "procedural posturing," and conceded countries are "Not yet close" to any substantive agreement.

Other officials were more blunt.

"I regret to report we have been unable to reach agreement," John Ashe of Antigua, chairman of one negotiating group, reported to conference Wednesday morning.

In those overnight talks, the American delegation apparently objected to a proposed text it felt might bind the United States prematurely to reducing greenhouse gas emissions, before the U.S. Congress acts on the required legislation. U.S. envoys insisted, for example, on replacing the word "shall" with the conditional "should."

"A lot of things are in play," said Fred Krupp of the U.S. Environmental Defense Fund. "This is the normal rhythm of international negotiations."

Hundreds of protesters marched on the suburban Bella Center, where lines of Danish riot police waited in protective cordons. Some demonstrators said they wanted to take over the global conference and turn it into a "people's assembly," and as they approached police lines they were hit with pepper spray.

Police said 260 protesters were detained.

Television pictures showed a man being pushed from the roof of a police van and struck with a baton by an officer.

Tens of thousands rallied in the streets of the Danish capital last weekend, demonstrating growing public awareness of the worldwide danger of ever-rising temperatures. Scientists say global warming will lead to the extinction of plant and animal species, the flooding of coastal areas from rising seas, more extreme weather, more drought and diseases spreading more widely.

The Copenhagen talks so far have been marked by sharp disagreements between China and the United States, and between rich and poor nations. After nine days of largely unproductive talks, the lower-level delegates were handing off the disputes to environment ministers in the two-week conference's critical second phase.

Organizers still hope break deadlocks that threaten to leave the meeting with no major accomplishments to be presented to President Barack Obama, Chinese Prime Minister Wen Jiabao and more than 110 other world leaders arriving for Friday's finale.

The lack of progress disheartened many, including small island states threatened by rising seas.

"We are extremely disappointed," Ian Fry of the tiny Pacific nation of Tuvalu declared on the conference floor. "I have the feeling of dread we are on the Titanic and sinking fast. It's time to launch the lifeboats."

Others were far from abandoning ship. "Obviously there are things we are concerned about, but that is what we have to discuss," Sergio Barbosa Serra, Brazil's climate ambassador, told The Associated Press. "I would like to think we can get a deal, a good and fair deal."

Governments had weeks ago given up hope of concluding a finished treaty at Copenhagen and aimed instead at establishing a framework, through decisions here, for negotiating more formal agreements next year.

Much of the uncertainty in the Copenhagen talks stems from how slowly the first U.S. legislation to cap carbon dioxide emissions is moving through Congress. Passage of a U.S. climate change bill is expected no earlier than next spring — and many other nations are unwilling to make their final commitments until the U.S. does.

The draft texts being debated behind closed doors in Bella Center hinge on four key issues, and negotiating views are generally divided between rich nations and developing ones.

EMISSIONS:

Industrialized nations are under pressure to cut back even more on emissions of carbon dioxide and other global-warming gases, while major developing countries such as China and India are being pressed to rein in the growth of their emissions. Environmentalists and poorer nations say richer countries should reduce their greenhouse gas emissions by 40 percent or more by 2020, compared with 1990 levels, to avoid serious climate damage. The European Union has pledged 20, possibly 30 percent. The U.S. has offered only a 3-to-4 percent cut.

FINANCING:

Richer nations have discussed a "prompt-start" package of $10 billion a year for three years to help developing nations adjust to the impact of global warming and switch to clean energy. Developing nations want to see commitments by wealthy nations for years more of long-term climate aid financing. Expert studies say hundreds of billions of dollars will be needed each year, and the developing nations are trying to establish stable revenue sources, such as a global aviation tax.

MONITORING:

The U.S. and developed nations want some kind of international verification of emissions actions by developing nations. China, India and others are resisting what they consider potential intrusions on their sovereignty.

LEGAL FORM:

For Europe, Japan and other developed nations, new, deeper emissions cuts will take the form of an extension of quotas under the 1997 Kyoto Protocol. The U.S., which rejected Kyoto and wants to remain outside it, likely to be included in a separate package that also deals with major developing countries. The level of legal obligation on each "track" may vary, particularly since the big developing countries — China and India — do not want to be bound by any international treaty to carry out their pledges of emission cuts. They prefer voluntary goals.

Fox News' William LaJeunesse in Copenhagen, and The Associated Press, contributed to this report.