Secretary of State Hillary Clinton made the announcement at a special meeting of the UN General Assembly on August 19 that focused on the international aid response to the flooding.
"On behalf of President Obama and the American people, I want to state our resolve to help Pakistan meet the immediacy of this crisis and then to recover from it,” Clinton said.
"I want the people of Pakistan to know that the United States stands with you during this crisis, that we will be with you as rivers rise and fall, we will be with you as you replant your fields and repair your roads. We will be with you as you meet the long term challenges to build a stronger nation and a better future," she added.
The new amount brings the U.S. aid contribution to $150 million. But the UN says the total amount raised is far from enough.
Weeks of heavy rains have flooded fully 20 percent of the country and left more than four million people without shelter, according the UN figures. As estimated 8 million people need immediate assistance and are in life-threatening situations, from disease or starvation.
In total, some 20 million people have been affected by the rising waters. As the crisis has deepened, the government's capacity to provide help has been pushed to the breaking point. Islamabad has been heavily criticized for failing to respond quickly enough.
Local aid groups, the Pakistani Army, and international aid agencies have helped hundreds of thousands of people obtain food, shelter, water and medical care, but the distribution has been chaotic and reached only a fraction of those who need help.
Milan Sima, a Czech journalist on assignment in Sukkur, a large city in northern Sindh Province, said he saw people fighting over the little aid that was available.
"We witnessed that some there wasn't enough food for some of them. Then they brought them blankets -- these people have nothing so they fought to get one blanket -- the government car that had brought the aid had to leave because there was such a [chaos]," he told RFE/RL.
"It was so disorganized, they didn't even manage to distribute all the blankets. They had to leave because of the crisis situation that ruled there, I almost got beaten up there," he added.
Sima said he had asked an aid coordinator if people could expect to receive fresh water, or any kind of help, from the government and was told that the aid worker had nothing to offer "but moral support."
Pakistan's 'Hour Of Need'
In an emotional speech at the UN, Pakistani Foreign Minister Shah Mahmood Qureshi said his country was facing "a natural calamity of unprecedented proportions."
"Pakistanis are a resilient people. We are no strangers to challenges and difficulties," he said. "This is a nation that suffered the ravages of the 2005 earthquake and bravely bore the loss of 80,000 of our brethren. We are the people who have borne the brunt of the international fight against terrorism and extremism with relentless courage and determination."
But now, he said, Pakistan is looking to the international community in its "hour of need."
"We are the people that the international community looks towards as a bulwark against terrorism and extremism," he said. “This is the nation that now looks towards the international community to show a similar determination and humanity in its hour of need."
The UN has made a flash appeal for aid to its members to give as generously as they can, but the response has been much less than it was for other recent natural disasters, like the South Asian tsunami and Haiti earthquake.
UN Secretary-General Ban Ki-moon said the international community is "is only now beginning to understand the true scope of this disaster," and that the floodwaters were "a slow-motion tsunami" whose destructive power would continue to grow.
"International humanitarian organizations are straining every muscle to deliver," Ban said. "But they need massive additional support. Eight million people need food, water, and shelter. Fourteen million need health care with a special emphasis on children and pregnant women."
The Asian Development Bank has just announced it would redirect $2 billion of existing and planned loans for reconstruction. Saudi Arabia said it would donate $80 million, making it the second largest donor, behind the United States. The EU has pledged to send an additional $38 million on top of a previous package of some $50 million worth of aid.
Ban urged donors to follow their pledges with action. "We have issued an emergency appeal for $460 million over next 90 days. We already have more than half, about 60 percent, thanks to the generosity of key donors," he said. "But all of these resources are needed and they are needed now. Your pledged today must be followed up with action -- action that delivers change on the ground."
The humanitarian suffering has been compounded by fears that insurgents will take advantage of the chaos and misery to increase their numbers. Islamist charities -- at least one of which has alleged links to terrorism -- have been active in the flood-hit areas.
Pakistani President Asif Ali Zardari has warned that the catastrophe "give[s] strength to forces who do not want a state structure."
written by Heather Maher and Golnaz Esfandiari in Washington, D.C., with agency reports