MARJAH, Afghanistan - Outnumbered and outgunned, Taliban fighters are mounting a tougher fight than expected in Marjah, Afghan officials said Sunday, as US-led forces converged on a pocket of militants in a western section of the town. With fighter jets, drones and attack helicopters roaring overhead, Marine and Afghan companies advanced on a 2-square-mile (5.2-sq. kilometer) area where more than 40 insurgents were believed holed up. "They are squeezed," said Lt. Col. Brian Christmas, commander of 3rd Battalion, 6th Marine Regiment. "It looks like they want to stay and fight but they can always drop their weapons and slip away. That's the nature of this war." US officials signaled their intention to attack Marjah, a major Taliban supply and opium-smuggling center, months ago, apparently in hopes the insurgents would flee and allow the US-led force to take over quickly and restore an Afghan government presence. Instead, the insurgents rigged Marjah with bombs and booby traps to slow the allied attack, which began Feb. 13. Teams of Taliban gunmen stayed in the town, delivering sometimes intense volleys of gunfire on Marine and Afghan units slogging through the rutted streets and poppy fields. Afghan Defense Ministry spokesman Gen. Mohammad Zahir Azimi said the U.S. and its allies had expected the Taliban to leave behind thousands of hidden explosives, which they did. But they were surprised to find that so many militants stayed to fight. "We predicted it would take many days. But our prediction was that the insurgency would not resist that way," Azimi told The Associated Press in Kabul. In a statement Sunday, NATO acknowledged that insurgents were putting up a "determined resistance" in various parts of Marjah, although the overall offensive is "on track."