U.N. talks on global warming are wrapping up in Peru, but a divide between rich and poor countries and how to divvy up targets to reduce greenhouse gases is a key sticking point that has remained unresolved.

U.S. Secretary of State John Kerry has acknowledged that the issue is "hard fought and ... complex," but he says it is crucial that the targets be agreed on before next year's summit in Paris. The talks in Peru end today.

"[If] it weren't hard, this would have been solved awhile ago," Kerry said Thursday in Lima. "But the fact is we simply don't have time to sit around going back and forth about whose responsibility it is to act. Pretty simple folks: It's everyone's responsibility."

He said a failure to act would represent a "massive, collective moral failure of historical consequences."

The BBC reports:

"Many developed countries want to see a change in the way the nations are classified in the UN process."Until now, the rich have been obliged to take on commitments to cut emissions while the poor have not."Countries such as the US say that the old divisions are outdated and they want everyone to take on some form of obligation."

In words that appeared aimed primarily at India and China, two of the world's largest contributors to greenhouse emissions, Kerry said it's vital that no country get a "free pass."

"I know this is difficult for developing nations. We have to remember that today more than half of emissions are coming from developing nations, so it is imperative that they act too," he said.

The Associated Press writes:

"China and other major developing countries oppose plans for a review process so the pledges can be compared against each other before the summit."Rich countries are resisting demands to include promises of financing to help poor countries tackle climate change."

Other sticking points include a clause in the text of the report outlining a principle known as "loss and damage," The Guardian reports. It adds:

"This is the idea pushed by some developing countries that they should receive financial compensation for the damage caused by extreme weather which has been exacerbated by rich countries' historical emissions."Developed countries are unsurprisingly not keen on it, and will point to their $10bn contributions to the separate Green Climate Fund, designed to help poor countries cope with global warming."Copyright 2016 NPR. To see more, visit http://www.npr.org/.