"Three days of heavy rains and flash floods have killed at least 408 people in Pakistan, authorities said Friday, as rescue teams struggled to evacuate thousands of stranded villagers from submerged hamlets and towns in the country's northwest.Swollen rivers washed away mud-hut villages and wrecked bridges, roads, hospitals and communication networks across the country's northwest province of Khyber-Pakhtunkwha. The death toll was the highest in the northwest, where Information Minister Mian Iftikhar Hussain said the destruction was the ""worst natural calamity in the province's history. ""By Friday, Pakistani authorities had also turned their attention to the south section of Punjab province, the country's heartland, where bloated rivers were submerging thousands of acres of farmland and shutting down roads.Authorities said 20 helicopters and 100 boats were being used to rescue as many as 400,000 stranded villagers in dire need of food and drinking water. U.S. Ambassador to Pakistan Anne Patterson said the U.S. was making available an additional seven helicopters for rescue efforts."