ISLAMABAD, Pakistan — Floodwaters surged into Pakistan's heartland and swallowed dozens of villages Tuesday, adding to a week of destruction that has already ravaged the mountainous northwest and killed 1,500 people.
The rush of muddy water over river banks in Punjab threatened to destroy vast stretches of crops that make the province Pakistan's breadbasket, prompting the U.N. to warn that an estimated 1.8 million people will need to be fed in the coming weeks.
Adding to the misery, fresh rains in the northwest threatened to overwhelm a major dam and unleash a new deluge, while rescue workers struggled to deliver aid to some 3.2 million people affected by the floods despite washed-out bridges and roads and downed communication lines.
The catastrophe, which started almost a week ago, is likely to deepen as more rains are expected and conditions are ripe for the outbreak of diseases. It has also called into question once again President Asif Ali Zardari's effectiveness and commitment to stabilizing U.S. ally Pakistan.
Zardari is already juggling many risky issues, from a Taliban insurgency to chronic power cuts in the nuclear-armed nation.
Pakistani authorities are struggling to help victims of the flooding, many of whom have lost their homes and livelihood and say they had not received any official warnings that raging waters were heading their way.
But the government issued flood warning on Tuesday as rising water levels threatened to overwhelm one of the country's biggest dams.
Disaster officials asked residents in the northern outskirts of Peshawar city, near the Warsak Dam, to leave their homes.
"If needed, forced evacuation will be started," said Adnan Khan, a spokesman for the Disaster Management Authority of Khyber-Pakhtoonkhwa province.
Dr. Muhammad Rafiq, program specialist for UNICEF in Peshawar, described to msnbc.com how the initial rushing floodwaters in the surrounding districts destroyed people's mud homes, leaving debris in their wake.
He said the approaching floods were announced from mosques in the middle of the night and people ran from their homes, leaving almost everything behind.
"Buffaloes and cows were tied to trees [when people fled] and they died when the water rose," Rafiq said. "It is summer, so their corpses are swollen from the heat and starting to burst."
Fears of a cholera outbreak are high, as contaminated water from dead animals quickly spreads disease — though there have not been any reported cases so far, Rafiq said.
UNICEF has been aggressively distributing leaflets and making regular announcements over local radio stations to educate people about dirty water and cholera, Rafiq said.
The U.N. organization has also been providing bottled water and water tanks to communities affected by the floods, and Rafiq said almost half a million people in Peshawar now have regular access to clean drinking water through UNICEF.
"The government doesn't have that much capacity or resources to reach these people," Rafiq said. "They obviously need the help of the international community."
Anger at government response
Many flood victims are unhappy with their government's response to the disaster.
About 300 people blocked a major road in the hard-hit Nowshera district to protest at receiving little or no aid, witnesses said.
Anger is spreading in towns such as Charssada. A Reuters reporter saw people attacking trucks distributing relief items. Police then charged at them with batons.
Bistma Bibi, 65, who lost two grandsons in the floods, accused government relief workers of only looking out for friends or relatives.
"I came here at 5 o'clock in the morning. I did my best. I begged and fought but got nothing. They're giving them (supplies) to their people," she said.
UNICEF spokesman Abdul Sami Malik said 1.3 million people were severely affected by the floods in the northwest.
Aid agencies and Pakistani government officials will meet on Tuesday to determine whether to make an urgent international appeal for help, he said.
U.S. sends aid
Both the U.S. and the U.N. have pledged $10 million to help Pakistan deal with the disaster and have provided relief supplies.
The U.S., which is keen to win friends in the country, has also helped Pakistan survey flood-stricken areas with reconnaissance aircraft and plans to send six military helicopters from Afghanistan to help with the relief effort, the U.S. military said in a statement.
"It is vitally important we try to help those who have been tragically affected by the massive flooding," said the top NATO commander in Afghanistan, Gen. David Petraeus.
But the U.S. has competition. At least one extremist group — a welfare organization allegedly linked to the Lashkar-e-Taiba militant network — is also helping survivors. The group, Falah-e-Insaniat, has previously helped civilians after other disasters.
Islamist groups played a key role in the relief effort following a 2005 earthquake in Kashmir that killed 75,000 people.
Pakistan's government faces militants who have proven resilient, carrying out suicide bombings despite a series of offensives the army said had weakened them.
More monsoon rains to come
Authorities forecast more of the heavy monsoon rains that have been lashing the area for the past week. Pakistan's National Disaster Management Authority said more than 29,500 houses were damaged and a key trade highway to China was blocked by flooding.
President Zardari is currently in Europe on a state visit, a trip that has angered both ordinary Pakistanis and political parties, some of which are trying to organize protests over his departure during this trying period.
His administration has faced cascading crises over the last few weeks, from the worst ever domestic plane crash on the edge of the capital to leaked reports on Islamabad's alleged support for militants battling U.S. troops in Afghanistan, to diplomatic rows with Britain.
Stability in Pakistan is vital to U.S. interests in the region. Washington believes Islamabad can help weaken the Taliban insurgency raging in Afghanistan by cracking down on Afghan militants who cross over the border to attack U.S. troops.
Pakistan's civilian governments have long been perceived as riddled by corruption and largely ineffective, leaving the powerful military to step in during troubled times.
Waters have receded in some flooded areas. But UNICEF's Malik expressed concern that waters were spreading from the worst hit province of Khyber-Pakhtunkhwa to Pakistan's Punjab heartland, the major food-producing province, as well as the Sindh region.
"What we have heard from Punjab is that 50,000 people have already been displaced and 200,000 people are being evacuated from Sindh," he said.
"In case of further rain, they expect that out of 23 districts in Sindh, 19 will be affected."
Officials said it was too early to estimate the damage the floods had caused to the economy.
Reuters and The Associated Press contributed to this report.