Government forces pounded rebel defenses with airstrikes, helicopter attacks and ground assaults as heavy fighting across northern Sri Lanka killed 47 Tamil Tiger fighters and left 13 soldiers dead or missing, the military said Wednesday. A rebel affiliated Web site claimed the Tamil Tigers had killed as many as 75 government soldiers in the recent fighting. The intense battles came amid a punishing government thrust into rebel-held territory in recent weeks that has forced the guerrillas to abandon large parts of their de facto state and a succession of key bases and towns to the advancing military offensive. The fighting has displaced tens of thousands of civilians, sending them fleeing deeper into rebel territory. On Tuesday, troops captured the town of Mallavi, which lies along an important access road in the region and which the military described as an "administrative hub" for the rebels. Battles raged Wednesday in the Nachchikuda area, deep inside the rebels' heartland of Kilinochchi, where Tamil Tiger fighters had built a dirt berm nearly 15 kilometers long and two meters high, military spokesman Brig. Udaya Nanayakkara said.