CAMP DWYER (AFP/Reuters) - Thousands of US Marines poured into Afghanistans Taliban heartlands Thursday, quickly capturing a district in the first major assault of President Barack Obamas new war plan. Dozens of aircraft ferried out the Marines from bases before dawn, aiming to take control of insurgent bastions of Helmand province in the countrys south ahead of landmark Afghan elections next month. Involving nearly 4,000 Marines, the air and ground assault was their first major operation since they arrived in Afghanistan as part of Obamas aggressive new strategy to turn the tide on a dragging conflict with the Taliban. Within hours Marines and Afghan troops had hoisted the Afghan flag in the southern Khanishin district, entering the main town with no resistance, Afghan commanders said. The enemies have fled, Afghan army corps commander General Shair Mohammad Zazai told AFP, adding troops had told the locals they would stay to maintain security, a key tenet of the revised strategy. Khanishin, towards the border with Pakistan across which Taliban travel, was one of a handful of districts in opium-growing Helmand where the Taliban held sway, establishing a proxy administration and justice system. But the Marines also counted their first fatality with one killed in hostile fire, spokesman First Lieutenant Kurt Stahl said without providing details. The helicopter insert has put all troops on the ground now in Garmser and Nawa, Stahl said, referring to districts that are key targets of the assault in the desert. Half of the objectives have been secured by nightfall, ahead of schedule. Slight resistance has been met, he said. It was the Marines biggest battle since Fallujah in Iraq in November 2004 and believed to be the largest joint operation in Afghanistan since March 2007 when British forces led 5,500 troops elsewhere in Helmand. But it was reportedly dismissed by the Taliban, with the Afghan Islamic Press quoting a spokesman as saying that previous operations had not yielded success for the armed forces. We are resisting but would adopt all kinds of war tactics to the situation, spokesman Yousaf Ahmadi was quoted as telling the agency. In one small part of the operation, a fleet of helicopters lifted about 300 Marines from a desert camp called Dwyer at dawn, their commander confident they would have cleared a key road, secured a bridge and met villagers by evening. What makes Operation Khanjar different from those that have occurred before is the massive size of the force introduced, the speed at which it will insert, Marine commander Brigadier General Larry Nicholson said. The forces pushed south down the Helmand River valley, deep into insurgent-held areas where foreign troops have failed to establish a presence despite ousting the Taliban from power in 2001. Our aim is for us to be meeting local people within hours, and thats what well be doing for the next seven or eight months, Nicholson told AFP. Commanders said they would persuade locals that the Afghan security forces - backed by Western troops - offered them a better long-term future than the hardliners. The Afghan armys Zazai told AFP the operation would establish security so that people can go and vote with confidence and without fear. Authorities have been concerned that the Taliban could undermine Afghanistans second-ever presidential vote with violence and intimidation. The Marines say Operation Khanjar will be decisive and is intended to seize virtually the entire lower Helmand River valley, the heartland of the Taliban insurgency. In swiftly seizing the valley and holding ground there, commanders hope to accomplish within hours what overstretched NATO troops had failed to achieve over several years, and help secure Afghanistan for an Aug 20 presidential election after years of stalemate. The intent is to go big, go strong and go fast, and by doing so we are going to save lives on both sides, Brigadier-General Larry Nicholson, commander of the Marines in southern Afghanistan, told his staff before the operation. This is a big, risky plan, Nicholson said. It involves great risks and amazing opportunities. These are days of immense change for Helmand province. Were going down there, and were going to stay - thats what is different this time. Our actions will allow voter registration in areas where there has been none, he told commanders and embedded reporters. The Taliban have vowed that its thousands of fighters in the south would fight back, even though only minor skirmishes were reported in the early stages. Thousands of Taliban mujahideen are ready to fight against US troops in the operation in Helmand province, Mullah Hayat Khan, a senior Afghan Taliban commander, told Reuters in Pakistan by telephone from an undisclosed location. The Taliban said in a later statement one of their fighters had been killed and two wounded. Quoting spokesman Qari Mohammad Yousuf, it said, 11 foreign troops were killed and wounded. The goal of this operation is to retake control of areas which are not in government control and will continue until the goal is achieved, the Afghan defence ministry added. Meanwhile, White House National Security Adviser James Jones has warned US commanders in Afghanistan that they will not receive more troops beyond those already promised by President Barack Obama. There was talk about coming in with more requests, Jones told McClatchy, the parent company of a group of US newspapers, on Wednesday following a tour in Pakistan, India and Afghanistan. However, he noted, everybody had their day in court, so to speak, before the president made his decision. We signed off on the strategy, and now were in the implementation phase. In a separate interview published Thursday, the top American military officer retorted that no limits had been placed on the number or types of troops that General Stanley McChrystal, the new US commander in Afghanistan, can request. Admiral Michael Mullen, the chairman of the US Joint Chiefs of Staff, said McChrystal was leading a 60-day assessment of the campaign in Afghanistan and had been advised to tell Obama, Mullen and Pentagon chief Robert Gates: Heres what I need. There are no preconditions associated with that, Mullen told The Washington Post. Hes... been told, 'In this assessment, you come back and ask for what you need. There are certainly no intended limits with respect to that kind of request.