Coalition forces led by U.S. troops are gaining ground in Afghanistan in the biggest offensive there since 2001.

Military commanders have raised the Afghan flag in the bullet-ridden main market in Marjah. But fighting remains intense in other parts of the Taliban stronghold.

"We're seeing more fortified positions. They're standing their ground, essentially," Lt. Josh Diddams said. "You don't know where you're going to get a little pop up of insurgents who are going to stay and fight."

Marjah is the hub of the Taliban's southern logistics and drug-smuggling network. Five NATO service members and one Afghan soldier have been killed since the attack on Marjah.

"About 40 insurgents have been killed," Helmand Gov. Gulab Mangal said.

NATO hopes to rush in aid and public services as soon as the town is secured to try win the loyalty of the population.