In some places, the water covers everything, dotted only by the tops of mango trees. Even here, with homesteads and roads on slightly raised lands, mud-brick houses have dissolved and all that remains are pitiful piles of debris where they once stood. Livestock and people camp on dirt roads that are often the only dry spot between acres of water. People cram into boats ferrying between villages, while a few motorbikes wend their way through the shallows. As Pakistan grapples with a disaster that has left millions homeless and many more cut off without food or clean water, the urgency of the situation was made clear to Sen. John Kerry, the Massachusetts Democrat who broke up a visit to Afghanistan to view the flood damage here Thursday. He flew over a vast expanse of flooded villages in Punjab province with Pakistan's president, Asif Ali Zardari, as the waters spread across the plain for miles; crowds swarmed at the edge of their landing pad. More than 1,100 people were housed in neat blue tents in an army compound, but their anxiety and frustration was palpable. As Pakistani officials briefed Kerry beside his helicopter, the governor of Punjab asked aloud whether the people were very angry. 'Naturally they are angry,' the district commissioner, Hassan Iqbal, answered. Zardari frowned. Both here and at home, U.S. officials spoke of the vast humanitarian task ahead, hoping to bolster the relationship between the two nations, which is widely viewed as critical for stability in the region. Secretary of State Hillary Rodham Clinton urged countries to step up their response to the devastating floods, pledging an additional $60 million in aid. That raised the total U.S. commitment to $150 million. Speaking to a special session of the U.N. General Assembly on Thursday, she referred to the feebleness of the global fundraising effort so far. 'I realize that many countries, including my own, are facing tough economic conditions and very tight budgets,' Clinton said. 'And we've also endured an unrelenting stream of disasters this year -- from the earthquake in Haiti to the wildfires in Russia. But we must answer the Pakistani request for help.' Closer to the devastation, Kerry spoke at an air base where U.S. Marines and members of the Pakistani army were flying joint missions to take food to the northern mountain valley of Swat and rescue stranded villagers. 'All of us are cooperating to deal with insurgency and violence,' Kerry told Marines and Pakistani troops in a hangar at the base. 'This is an additional test.' Last year, the picturesque hillsides and towns in the Swat Valley were transformed into a battleground when government troops tried to drive out the Taliban forces that had set up a haven there. Millions were displaced, fleeing both the Taliban and the shelling and fighting that followed as the Pakistani military retook control last spring. But months after residents began returning, the flooding has ruined their hopes for a respite from the relentless upheaval and renewed their fears that Taliban forces might now seize on the disorder to re-establish a foothold. In helping the mountainous region now, Kerry openly acknowledged a double concern. 'The objective is humanitarian, but obviously there is a national security interest,' he said. 'We do not want additional jihadis, extremists, coming out of a crisis.' In Pakistan's northwest, some hard-line Islamic groups have been providing shelter and food to flood victims, exploiting gaps in the government's slow and haphazard initial response. More aid is now flowing, but the concerns remain. While in New York to draw the world's attention to the crisis, Pakistan's foreign minister, Shah Mehmood Qureshi, said that extremist organizations would capitalize on any vacuum in humanitarian assistance. 'Obviously, they would like to exploit the situation,' he said. 'The possibility is there, and we have to guard against it.' Trying to cast a positive light on the calamity, Kerry suggested that the humanitarian effort would force the nation's civilian government to step up to the challenge and improve its performance to meet the needs of the population. 'There is a real willingness to build capacity, and that can strengthen the government,' he said. Yet the fear is that another disaster after years of turmoil -- Pakistan lost 73,000 people in a devastating earthquake in Kashmir in 2005 and has suffered thousands of casualties in the war against Islamist militants since 2007 -- will set the country back decades. 'The economic impact is going to be huge,' said Anne W. Patterson, the U.S. ambassador to Pakistan, who was traveling with Kerry. Pakistan was expecting a food surplus this year, so even with the huge losses of food and grain from the floods the country could probably still feed itself, Patterson said. But food prices will soar, she said, affecting the poorest sector of the population. 'The price rises are going to be terrible and the poor people are going to be crowded out,' Patterson said. Here in Jampur, Nazar Hussein, 35, described how his family of nine had to flee in the night, carrying the children through chest-high water. 'We were in our house sleeping; it was about 9 p.m. at night when we heard the neighbors shouting,' he said. 'We were very frightened,' he added as his small daughters pressed against him. His house, built of mud bricks and plaster, had collapsed under the weight of the water, he said. Hussein, a laborer, said that even when the water receded he would not be able to afford the $6,000 it would cost to rebuild his house. 'We are waiting for the government,' he said. 'Without government help we cannot do it.' To enable the reconstruction effort, Zardari said, 'we will provide debit cards so they can receive money directly and rebuild their houses.' The system of paying money directly to households so that they can do their own rebuilding worked well after the earthquake, as well as for people displaced by fighting last year. But officials were still working out how much damage has been done. Although the waters were receding in Punjab province, they were still rising in the southernmost province of Sindh, where the waters will eventually spill into the Arabian Sea. The scale of the disaster is clearly tremendous. On Thursday, the United Nations raised the number of people left homeless by the floods to 4.6 million. 'This is a rough estimate and includes hundreds of thousands still on the move,' said Maurizio Giuliano, the U.N. spokesman in Pakistan. 'In this context, we have decided to increase the number of targeted beneficiaries for tents and plastic sheeting from the initial figure of 2 million to at least 6 million.' The Asian Development Bank, meanwhile, said it would loan Pakistan $2 billion to rebuild from the floods, which have covered at least one-fifth of the country and claimed as many as 1,600 lives. Clinton also urged U.S. families to donate. 'More than 20 million Pakistanis have been affected by the worst natural disaster in Pakistan's history,' she said. 'The enormity of this crisis is hard to fathom, the rain continues to fall, and the extent of the devastation is still difficult to gauge.' 