The official, who spoke on condition that he not be named because Washington has not yet unveiled its pledge, also said he expected the Paris conference on Thursday to raise more than US$15 billion in total pledges, including the US contribution.

The US pledge, to be announced by Secretary of State Condoleezza Rice, will be less than the US$11 billion that the Bush administration had hoped to secure from Congress, the US official said.

It is not clear how much of the money pledged in Paris will reflect fresh commitments from the donor community.

US Assistant Secretary of State Richard Boucher told reporters the US contribution would reflect money that the Bush administration had already made public in its budget requests to the US Congress over the last two years.

He also said the United States had encouraged other donors to include in their pledges money that they have promised since the last Afghan donors conference in London in 2006, when he said $10.5 billion was committed to Afghanistan.