A clearly frustrated President Barack Obama displayed impatience with world leaders' failure to reach a new climate accord, urging them to accept a less-than-perfect pact while offering no new US concessions.
Mr Obama said the US has acted boldly by vowing to reduce heat-trapping gasses and help other nations pay for similar efforts.
But he indirectly acknowledged that some countries feel the US is not doing enough, and he said an imperfect accord is better than an impasse.
"No country will get everything that it wants," Mr Obama said in a brief address to the 193 nations gathered to cap a climate summit stalemated after two weeks of talks.
Without mentioning China specifically, he addressed Beijing's resistance to making its emissions-reduction pledges subject to international review.
"I don't know how you have an international agreement where we all are not sharing information and making sure we are meeting our commitments," Mr Obama said. "That doesn't make sense. It would be a hollow victory."
Mr Obama later met privately with Chinese Premier Wen Jiabao for nearly an hour to discuss emissions targets, financing and transparency. A senior Obama administration official said the two took "a step forward," which led them to direct aides to work on a possible agreement.
In his speech to the assembled leaders, Mr Obama said: "We are running short on time."
"We are ready to get this done today," he said. "But there has to be movement on all sides."
And yet Mr Obama arrived in snow-covered Copenhagen with no new proposal from the US side. Some had hoped he might increase Washington's emissons-cut pledge, now only a fraction of those from other developed countries, or put a specific dollar amount on America's expected contributions to short or long-term aid funds to help poorer nations deal with the effects of climate change. Obama planned to spend only about nine hours at the summit. He was holding a series of large and small meetings with various leaders, including those from China and Russia.