Snipers, booby traps, and a maze of mines have hampered progress as U.S. Marines, along with British and Afghan troops push their way into the Taliban stronghold of Marja.
"Some units have been heavily engaged in day long firefights," Capt. Abraham Sipe of the U.S. Marines-Region Command South told ABC News.
Sipe expressed surprise at the high number of IEDs [improvised explosive devices] they had encountered. Disarming them dramatically slows down the operation.
"This is a steady, methodical process. We have to be deliberate to safeguard the lives of the Marines and their Afghan partners," Stipe said.
Five to six explosions an hour can be heard in Marja, nearly all believed to be controlled detonations of booby traps.
In a city where all the roads and buildings are made of dirt, the bombs can be buried into anything and the Taliban planted explosives in doorways, paths, windows and along canals. The invaders are using bomb sniffing dogs, minesweepers and anti-bomb devices that roll in front of vehicles to set off any bombs.
Nevertheless, after a path was cleared for an armored vehicle to reach a bridge into Marja, it struck a mine on the bridge, according to ABC News' embedded reporter. No one was hurt in the explosion.
While the Marines believe they have taken control of all the key buildings and major intersections of Marja they are not yet sure exactly which parts of the town remain hostile.
"We have achieved our initial objectives and have presence in a fair bit of the area, but we still have a large area to clear," Stipe said.
As the remaining Taliban are forced into smaller areas of the city, the amount of sniping and firefights has picked up.
"In some places, for one reason or another, they have decided to stand and fight," Stipe said.
Witness Abdul Khaliq told ABC News that he had heard frequent gunfire in the center of Marjah today and that the main fighting is in and around the market area.
Khaliq added that U.S. and British armored vehicles were having difficulty entering the town with many stalled at key bridges that are rigged with homemade bombs.
Gen. Stanley McChrystal, the top U.S. commander in Afghanistan, told ABC News he was pleased with the operation so far.
"There still remains plenty of danger and hard work ahead. But I will say how proud I am of the Afghan and coalition troops who are performing impressively well given the scale and complexity of the mission," McChrystal said.
Lt. Col. Mark Dietz, deputy commander of the Marines in Helmand, told BBC news that invading forces had met with considerably less resistance than initially anticipated.
Original estimates from intelligence indicated that there were between 400-800 insurgents holed up in the town that Dietz described as the "last bastion of the Taliban" in the Helmand valley.
"There have been several pockets of stiff resistance," Dietz said.
Twice since Sunday the Marines have tried to reach the bazaar area in southern Marja, and both times they have been met with heavy gunfire forcing them to call in Harrier jets and attack helicopters with Hellfire missiles.