The top US climate negotiator on Tuesday gave an upbeat assessment of ties with China, saying the world's two largest emitters found ways to work together at UN-led talks in Durban, South Africa.

The tone contrasts with a recent harder line toward China from US President Barack Obama's administration, which has voiced concern over Beijing's record on issues ranging from military spending to trade to human rights.

"Dynamic US-China? I think actually quite good," Todd Stern, the US envoy on climate change, told reporters on a conference call about the marathon talks in Durban.

"Countries all carry their own interests and their own red lines, their own concerns in any negotiation, and ours are not the same as the Chinese," he said.

"I think that we actually have a very positive and very substantive and very cordial relationship that's now for me three years old between the US and China," said Stern, who took office when Obama became president in 2009.

The Durban talks reached a general agreement to work toward the first climate treaty that has legal force and encompasses all nations by 2015.

US lawmakers have been pressing for years for China -- which has surpassed the United States as the largest producer of emissions blamed for climate change -- to face international obligations to fight climate change.

Former US president George W. Bush rejected the outgoing Kyoto Protocol in large part due to concerns that it only covers wealthy nations and not emerging economies.

In the midst of the Durban talks, China's top climate negotiator laid out conditions for a legally binding treaty which would include a renewal of carbon-cutting pledges by rich nations and aid for poorer countries.

India took a vocal role in the Durban talks, with Environment Minister Jayanthi Natarajan at one point vowing not to be "intimidated by threats or intimidation" by wealthy nations on the future of climate action.