More American helicopters arrived in Pakistan to help ferry aid to flood victims as U.N. Secretary-General Ban Ki-moon was expected to visit Sunday in areas affected by the disaster the government estimates has made 20 million people homeless.
Cholera has surfaced among survivors and aid workers warn that the waterborne disease could add to the death toll of about 1,500 people if allowed to spread.
A fresh surge of floodwater swelled the Indus River on Saturday, threatening previously spared cities and towns in the south.
The crisis has battered Pakistan's economy and undermined its political stability at a time when the United States needs its steadfast cooperation against Islamist extremism. The U.N. has appealed for an initial $460 million to provide relief to Pakistan but has said the country will need billions to rebuild once the floodwaters recede.
U.N. chief Ban was expected to visit flood-devastated areas Sunday, though his schedule was not clear.
The United States has so far donated the most to the relief effort, at least $70 million, and has sent military helicopters to rescue stranded people and drop off food and water. Washington hopes the assistance will help improve its image in the country - however marginally - as it seeks its support in the battle against the Taliban in neighboring Afghanistan.
"So far, if anyone has practically given us maximum help, it is America," Prime Minister Yousuf Raza Gilani said Saturday when a Pakistani reporter suggested the U.S. has done little since the crisis started.
Two additional U.S. Navy MH-53E Sea Dragon helicopters arrived in Pakistan on Saturday to support flood relief efforts, the U.S. State Department said. That brings to seven the total number of aircraft in Pakistan from the USS Peleliu, which is positioned in international waters in the Arabian Sea.
Operating in partnership with the Pakistan military, the U.S. aircraft have since Aug. 5 rescued more than 3,500 people and transported more than 412,000 pounds (186,000 kilograms) of emergency supplies, the State Department said.
Separately, U.S. missiles killed 12 people Saturday in a Pakistani tribal region filled with Islamist insurgents bent on pushing Western troops out of neighboring Afghanistan, showing that Washington is not willing to stop using a tactic that has fed its unpopularity here.
One case of cholera was confirmed among flood survivors in Mingora, the main town in the northwest's Swat Valley, U.N. spokesman Maurizio Giuliano said Saturday. But other cases were suspected, and aid workers are now responding to all those exhibiting acute watery diarrhea as if it is cholera, Giuliano said.
Cholera can lead to severe dehydration and death without prompt treatment, and containing cholera outbreaks is considered a high priority following floods.
The Pakistani crisis began in late July, when unusually heavy monsoon rains tore through the country from its mountainous northwest. Hundreds of thousands of homes have been destroyed. Agriculture has been severely hit, with an estimated 1.7 million acres (nearly 700,000 hectares) of farmland wiped out.
In a televised address to the nation Saturday, Gilani said 20 million were now homeless. He did not elaborate, and it was unclear how many of those people were briefly forced to leave their homes and how many had lost their houses altogether.
Fresh flood waves swelled the River Indus on Saturday, threatening nearby cities, towns and villages in southern Sindh province, said Mohammed Ajmal Shad, a senior meteorologist. The Indus was already more than 15 miles (25 kilometers) wide at some points Friday - 25 times wider than during normal monsoon seasons.
Authorities were trying to evacuate or warn people in Jacobabad, Hyderabad, Thatta, Ghotki, Larkana and other areas in Sindh province that so far have been spared floods.
Ghulam Sarwar said he, his wife and eight children had already fled the town of Thal because of flooding. Overnight, they had to get out of Jacobabad after the fresh warnings. Now they wait in a small tent relief camp on the edge of the city of Sukkur.
"Our whole world has been ruined by the flood, and the whole of Sindh is drowning," the 42-year-old said. "We do not know how long we will have to suffer."
The Pakistani government's reputation - already shaky to begin with - has suffered during the crisis, especially after the president decided to visit Europe as the crisis was unfolding. President Asif Ali Zardari has tried to make up for that public relations gaffe by meeting with flood victims in hard-hit areas since returning.
"We are with you. Pakistan is with you, and the people of Pakistan are with you," he told survivors at a relief camp in the northwest's Nowshera city Saturday. He promised the government would rebuild victims' homes.
Associated Press writers Asif Shahzad and Munir Ahmed contributed to this report from Islamabad.