U.S.-led NATO troops launched a crucial offensive on Saturday against the Taliban's last big stronghold in Afghanistan's most violent province and were quickly thrown into a firefight with the militants. Within hours of the operation getting underway, U.S. Marines at the tip of the assault battled with Taliban militants in Marjah, in Helmand Province, all the time facing the possibility of being blown up by booby traps rigged across the town. Marines engaged in a firefight with Taliban militants after the U.S. troops landed in helicopters near the town. They fired at least four rockets at militants who attacked from compounds. At least one Marine was wounded by shrapnel. More than two hours later, the area was still gripped by the firefight, with the Marines firing another large rocket. One family of civilians nearby was huddled in a room of their house, with the washing flapping on the line outside. A Reuters reporter said exchanges of fire -- with assault rifles crackling -- erupted initially about 300 metres away. Moments earlier, two large explosions resounded and a large black plume of smoke rose into the sky. The offensive began with waves of helicopters ferrying U.S. Marines into the city in the early morning hours. British troops then flew into the northern part of the surrounding Nad Ali district, followed by tanks and combat engineering units. "The first phase of the operation is proceeding very successfully. The Taliban have heavily booby-trapped the area, but there has not been any fierce fighting yet," Helmand Governor Gulab Mangal told a news conference. "We have seized 11 key locations in the district and the resistance from the insurgents has been subdued."