The United States said on Wednesday U.N. climate talks were making less progress than hoped because of a rift over poorer nations’ emission goals, and that other avenues might be needed to tackle climate change.

Negotiators from 177 governments are meeting this week in the north Chinese city of Tianjin trying to agree on the shape of the successor to the current phase of the Kyoto Protocol, the key U.N. treaty on fighting global warming, which expires in 2012.