The BBC's Frank Gardner, in Kandahar, says the homemade bombs have been planted in far greater numbers than Nato had anticipated.
Operation Moshtarak - targeting Taliban strongholds in southern Helmand province - has entered its third day.
Earlier, the Nato commander apologised after rockets killed 12 civilians.
Actually, nobody has been forced from anything. In a repeat of the same strategy that wore out the Soviets, the Taliban simply leave their bases and merge in with he general population, leaving the surge to waste time and money shelling empty buildings and tripping overt the booby traps. The US will declare victory and leave and the Taliban will repair their bases and the war will go on.