Secretary of State Hillary Clinton announced an additional US$60 million in US aid, bringing to US$150 million the amount pledged by the United States.

"The flooding has already affected more people than the Indian Ocean tsunami, the Haiti earthquake, and the 2005 Pakistan earthquake combined," she told a plenary session at the United Nations. "And as we meet, we fear that a new wave of water may be about to sweep through areas that have already been devastated by the floods."

She added, "We see 20 million members of the human family in desperate need of help. This is a defining moment -- for Pakistan, and for all of us.

She predicted the situation will worsen before getting better. "More than 800,000 houses have been damaged or destroyed; 2 million people have been forced to flee their homes; hundreds of bridges have been washed away, cutting off communities from relief supplies," she said.

Clinton called on Americans to contribute to the Department of State's Pakistan Relief Fund.

Pakistani Prime Minister Yousaf Raza Gilani has pledged to ensure relief funds end up in the right hands.

The United Nations has received less than half of the US$460 million it is seeking for relief efforts. Despite millions of dollars in support from other countries, the flow of aid is failing to keep pace with the need, aid agencies have said.