Fifteen US senators called Monday for an ambitious agreement at climate talks in Durban, South Africa, pledging that the United States will play a role in cutting greenhouse gas emissions.

The senators -- 13 members of President Barack Obama's Democratic Party and two independents -- made the appeal despite criticism in Durban that the world's top economy has yet to take major nationwide action on climate change.

The senators, led by Democrat John Kerry of Massachusetts, said that the impact of climate change was "occurring more quickly than previously predicted" and pointed to this year's drought believed to have killed thousands on the Horn of Africa.

"We are committed to doing our part to transition to a clean energy economy that decreases carbon pollution, creates jobs and builds resilience in vulnerable communities both at home and abroad," the senators wrote in a letter to Secretary of State Hillary Clinton.

The senators called for "a strong and ambitious package of outcomes from Durban," including action to move ahead on financial assistance to poor countries most vulnerable to rising temperatures.

"As the costs and effects of climate change continue to mount, it is critical that the US be an active part of an effective global response," the senators wrote.

The Durban talks run until Friday, with tensions high as the landmark Kyoto Protocol's requirements for wealthy nations to cut carbon emissions expire at the end of 2012.

The United States was the only major country to reject the Kyoto Protocol, with former president George W. Bush saying it was unfair by making no demands of emerging economies such as China, now the world's top emitter.

President Barack Obama has pledged that the United States will cut carbon emissions by around 17 percent by 2020 from 2005 levels. But a bill led by Kerry to mandate restrictions on emissions died in the Senate last year amid fierce opposition by the rival Republican Party.