US Marines came under attack from insurgents armed with sniper guns and rocket-propelled grenades as they geared up today to overwhelm a Taliban bastion in Afghanistan. Thousands of Marines along with foreign and Afghan soldiers are taking up position around the town of Marjah in Helmand, which officials say is one of the last areas of the southern province under Taliban control. The flow of residents fleeing the imminent offensive has slowed, provincial officials said, after loaded-down cars, trucks, tractors and buses clogged roads from Marjah to provincial capital Lashkah Gar for days. The operation, expected to begin in days, will be the biggest push since US President Barack Obama announced a new surge of troops to Afghanistan and one of the biggest since the 2001 US-led invasion defeated the Taliban regime. <br/>