Taliban forces advanced on the capital of the volatile southern Afghan province of Helmand on Tuesday amid fierce fighting with government forces that threatened to cut off a major highway and prompted many families to flee. The fighting near the town of Lashkar Gah comes three weeks after the Taliban won its biggest victory in the 14-year war, capturing the northern town of Kunduz and holding the city center for three days before government forces regained control. "Helmand's capital appears to be under serious military pressure," a Western official said. "We're hearing reports about civilians fleeing in large numbers." Helmand province is one of the world's biggest centers of opium cultivation, with a complex mix of warring tribal groups and Taliban insurgents creating a chronic problem for the Western-backed government. Provincial Governor Mirza Khan Rahimi said heavy fighting had been going on for two days in the district of Gereshk to the north of the city. The fighting has threatened Highway One, the main transport artery linking the major southern city of Kandahar with Herat. Farhad Dawary, head of the local Civil Societies Union, which represents non-government social organizations, said that after days of fighting, families were both fleeing to Lashkar Gah from outlying areas and trying to escape from the city. "There is fear among the people in Lashkar Gah, there are lots of rumors the city might fall," he said.