Moammar Gadhafi's seemingly routed troops still could extend Libya's civil war by weeks or months by resorting to urban warfare in the streets of Tripoli, though the embattled leader's forces appear to have done little to prepare for such a bloody last stand.
NATO airstrikes that have pounded Gadhafi's forces for months, largely in the open North African deserts, would be more challenging in the capital of 2 million people. But NATO officials have discounted the possibility of protracted resistance, pointing out that regime forces have simply melted away in recent days under relentless pummeling from the air and pressure from the advancing rebels. Rebel troops stormed the heavily fortified Bab al-Azizya presidential complex on Tuesday.
"There is no doubt that pro-Gadhafi forces are severely eroded," said Col. Roland Lavoie, spokesman for NATO's operational command in Naples. He said regime troops have been expelled from strategic military positions and lost control of a growing number of cities and villages.
He added, however, that some regime units continued to fight aggressively in Tripoli and that the situation in the capital remained "very, very dynamic and complex."
Gadhafi's son Seif al-Islam appeared in public Monday night and called on loyalist forces and citizens to rally together and oust the rebels who now occupy large sections of the capital.
It remains to be seen whether Gadhafi's troops can muster that kind of determination. The strongman's army has shown little initiative or ability on the battlefields to coordinate its attacks. Its command and control facilities _ including the presidential compound _ were pulverized by NATO bombs.
Neither Gadhafi nor his forces have given any indication that they are staging for urban battle in Tripoli. NATO officials have said they saw no signs of preparations for a determined defense, including the digging of trenches, construction of bunkers or other strongpoints.
If Moammar Gadhafi's troops do stage a last stand in Tripoli, house-to-house fighting with untrained and lightly armed opposition forces could quickly turn into a bloody quagmire worse than anything seen on the battlefields in the past six months of war.
Urban warfare was a defining aspect in some of the major battles since World War II: The Vietnam War's Battle of Hue in 1968, Beirut's civil war in the 1980s, the 1991 siege of Vukovar in Croatia by Serb units, the U.S.-led conflict in Mogadishu in 1993, Russia's battle with breakaway Grozny in the 1990s and the combat in Fallujah and other cities across Iraq.
Most of the cities involved were practically destroyed during the fighting because the attackers relied on heavy artillery fire and carpet bombing from the air to clear the defenders.
Col. Ljubomir Stojanovic, who served as Yugoslav army spokesman in the early 1990s, said combat in towns and villages was probably the most challenging and bloodiest of all forms of warfare.
Small groups of defenders can lay deadly hit-and-run ambushes as the attacking forces crawl forward, clearing streets house-by-house, and houses room-by-room, he said. Defenders only need the most basic weapons, such as small arms and rocket propelled grenades, to make it very costly for even well-trained units to advance inside a city.
In Vukovar, a force of 2,000 Croat soldiers was able to hold off a federal force 15 times that size for nearly three months, despite the attackers' massive superiority in armor, artillery and air power.
Clashes in populated areas generally result in heavy casualties, none more than the Battle of Stalingrad in 1942, which ranks as the bloodiest in the history of warfare. Nearly 2 million Soviets and Germans were killed or wounded in the five-month battle, which became a turning point in World War II.
"Urban warfare soaks up troops because it demands much manpower to secure any areas," said Martin Van Creveld, a military historian at Hebrew University in Jerusalem.
"It offers very great advantages for defense even against much larger forces," he said. "You can find every kind of shelter inside a city and if the enemy turns the buildings into rubble, this just provides even better cover."
Van Creveld said Israeli forces avoided entering Gaza during the 2008-2009 conflict because of their painful experience six years earlier fighting inside the town of Jenin on the West Bank, where they lost two dozen troops in a matter of days despite very weak opposition.
NATO, however, would be better equipped than armies of the past were to launch air attacks in urban environments. Some of its aircraft, including French Tigre and British Apache helicopter gunships and U.S. unmanned drones, are suited to close-quarter combat because of their precision-guided munitions.
Alliance strike jets can be configured to carry low-yield bombs such as the Brimstone anti-tank missile, which has small warheads that are designed to pinpoint and destroy targets without harming nearby civilians.