US Marines are trading gunfire and artillery shells with Taliban militants in the volatile southern province of Helmand, the world's largest poppy growing region. The 24th Marine Expeditionary Unit moved into the town of Garmser in late April. It's the farthest south US forces have been in Afghanistan in years. Marine commanders say the Taliban brought in arms and fighters in response, to protect the lucrative poppy fields that cover Garmser. The Taliban derives tens of millions of dollars from the poppy trade each year by taxing farmers and charging safe passage fees. The Marines originally planned to be in Garmser for only a couple of days, to open a road that leads to southern Helmand, near the border with Pakistan. But the 24th MEU decided to extend its stay to root out the fighters. After weeks of skirmishes with insurgents - who fired rockets and mortars at US positions several times daily - NATO officials say the militants fled the region late last month. A shura - a council of village elders - was held in Garmser for the first time in years.