MARJAH/WASHINGTON – US Marines, NATO troops, Afgan National Army (ANA) and Taliban insurgents exchanged gunfire on Thursday on the outskirts of Marjah, a southern insurgents stronghold where American and Afghan forces are expected to launch a major attack in the coming days. To the north, a US-Afghan force led by the US Army's 5th Stryker Brigade linked up with Marines yesterday, closing off a Taliban escape route to the nearby major city of Lashkar Gah. No casualties were reported in the scattered clashes, which broke out as Marines moved ever closer to the edge of the farming community of 80,000 people, the linchpin of Taliban influence in the opium poppy producing province of Helmand. Marines said the Taliban defenders were apparently trying to draw the Americans into a bigger fight before the US was ready to launch the main attack. "They're trying to draw us in," said Capt. Joshua Winfrey, 30, of Tulsa, Okla., commander of Lima Company, 3rd Battalion, 6th Marines. Through much of the day, insurgents repeatedly fired rockets and mortars at the American and Afghan units poised in foxholes around the town, 380 miles (about 610km) southwest of Kabul. "I am not surprised at all that this is taking place," said the battalion commander, Lt. Col. Brian Christmas. "We are touching their trigger-line," referring to the outer rim of the Taliban defences. The Taliban vowed yesterday to fight back with a "hit and run" guerrilla campaign against Western and Afghan forces preparing to storm one of their key strongholds in southern Afghanistan. The assault, dubbed Operation Mushtarak ("Together" in Dari) and expected to begin within days, aims to drive out the Taliban and replace their harsh rule with Western-backed Afghan government institutions. In a defiant statement on their website, the Taliban vowed to defend the town in the poppy-growing region of the central Helmand River valley, which they have controlled for years in tandem with drug traffickers. "The enemy is making a big deal of it. They try to sell it to the media as a big offensive in spite of the fact that Marjah is a small place," he said, adding: "The operation is not as big as they claim." Meanwhile, US Vice President Joe Biden said on Thursday that his greatest concern was not Afghanistan, not Iraq, nor the Iranian nuclear crisis, but Pakistan. "I think it's a big country. It has nuclear weapons that are able to be deployed. It has a real significant minority of radicalised population," Biden said in an interview with CNN. "It is not a completely functional democracy in the sense we think about it, and so that's my greatest concern."