SOOMRA PANHWARI, Pakistan — Torrential rain was forecast to lash flood-hit Pakistan Sunday, hampering the aid effort and threatening to deepen a crisis affecting 15 million people in the country's worst ever floods. The UN special envoy dispatched to help with the flood relief effort cancelled a flight to stricken areas and Prime Minister Syed Yusuf Raza Gilani also postponed his trip for a day because of the rain. At least 11 people were killed and 31 injured when a truck carrying flood evacuees fell into a ditch on Saturday after skidding off a slippery road in the northwestern district of Lower Dir, police officer Mumtaz Zareen said. Those uprooted from their homes in Sindh have been moved to government buildings, schools and tents, but many families in low-lying areas resisted evacuation, said irrigation minister Jam Saifullah Dharejo. Countries including Britain, China, Australia, France and the United States have pledged tens of millions of dollars in aid for victims of the nearly two-week-old disaster. The United Nations estimates at least 1,600 people have been killed by the floods that have ravaged the largely impoverished, insurgency-hit country, sweeping away entire villages. The flooding has threatened electricity generation plants, forcing units to shut down in a country already suffering a crippling energy crisis. In Khyber Pakhtunkhwa, head of flood relief operations Major General Ghayoor Mehmood said some 1,400 people have been killed, with 213 still missing. Flooding has spread to Indian-held Kashmir, where more than 130 people have died, while some parts of the Punjab are under six feet (two metres) of water, affecting nearly two million people, a senior crisis management official said. More than 252,000 homes are thought to have been damaged or destroyed across Pakistan and 1.38 million acres (558,000 hectares) of farmland flooded, and it could be weeks before electricity is fully restored.