Sixteen US commonweal organizations urged the United States not to block the ongoing climate change negotiation here in a letter to US Secretary of State Hillary Clinton, the international confederation Oxfam said Thursday.

The 16 groups, including Oxfam America and the US Environmental Defense Fund, said in the letter that the US positions on authorizing future climate talks and setting up the Green Climate Fund (GCF) would block the progress of seeking global collaboration.

They also called on the US delegation to cooperate with the parties concerned to narrow differences including the GCF, and to achieve the goal of confidence and trust building by the end of the conference.

Washington's rejection of the GCF broke the broad consensus reached in Cancun, Mexico, undermined the already achieved balance and might lead to a failure in establishing a viable fund management system, they said.

The GCF was agreed on at the 16th Conference of Parties to the United Nations' Framework Convention on Climate Change (COP) in Cancun last year. It requires that developed countries provide 100 billion US dollars to poorer countries by 2020 to help them cope with carbon emissions and adapt to climate change.

The United States has demanded that apart from developed countries, developing nations should also contribute to the fund. Another major issue is whether the private sector should be given direct access to the fund, as an equal partner with the other two main targets of the fund, mitigation and adaptation.