HELMAND PROVINCE, Afghanistan –NATO troops in Afghanistan launched their biggest offensive of the war early Saturday, attacking what they call the last Taliban stronghold in a war-scarred southern province.

Military officials said the offensive—dubbed Operation Moshtarak— got under way at 2 a.m. (4:30 p.m. ET Friday). By about 8 a.m. (10 p.m. ET Friday) two firefights had erupted between the Taliban and U.S. Marines in Marjah.

The offensive turned a main bazaar near the city center into a ghost town after residents were warned to leave the area. NATO forces said they are following a directive not to shoot at civilians, some of whom are still on the streets.

"Insurgents who do not accept the government's offer to reintegrate and join the political process will be met with overwhelming force," the International Security Assistance Force Joint Command said in a statement. "However, the strongest of measures will be taken to protect the civilian population."

Some of about 15,000 troops from the United States, United Kingdom, Canada and Afghanistan attacked Taliban targets in and around Marjah, a city of 80,000 to 100,000 where the Taliban has set up a shadow government, coalition military authorities said.

"Marjah is the last enemy sanctuary in the Marine area of operations," said Brig. Gen. Larry Nicholson, 2nd Marine Expeditionary Brigade-Afghanistan commanding general. "This operation is designed to reconnect the people of Marjah with the legitimate government of Afghanistan. We are fully partnered with the Afghan government for this operation, and we have the resources we need to be successful."

The Afghan government described the offensive - carried out in central Helmand with the Afghan National Army, Afghan National Police, ISAF Regional Command (South), and the Helmand Provincial Reconstruction Team - as "clearing" operations. Moshtarak, a Dari word for "together," symbolizes the fact that combined forces are serving alongside one another.

The coalition said its troops expected to confront up to 1,000 entrenched Taliban fighters. It expected foreign Taliban fighters to battle to the death but is prepared for local Taliban members in Marjah to try to escape.

“We will follow the enemies and bring them to justice,” said Gen. Mohiyiden Ghori of the Afghan National Army.

In the past few days, forces from Afghanistan, Britain and other nations have conducted air and ground operations to prepare for the assault and dropped leaflets in and around Marjah warning residents not to allow the Taliban to

enter their homes.

The allies had been unusually vocal in describing their plans for the assault. (Related: Why the military publicized operations)

“I think there’s a certain strength in the Pashtunwali culture just from laying it out there in saying, ‘Hey, we are coming. Deal with it,’” U.S. Marine Gen. Larry Nicholson has said.

Some of the 30,000 additional U.S. troops that President Barack Obama sent to Afghanistan will take part in the fight.

The goal is to force the Taliban from Marjah so that people there can live free of Taliban influence and drug traffickers in a province with a major source of the world’s opium. It’s an example of a U.S. strategy to focus on population centers and separate the Taliban from Afghan civilians. (Related: Why Marjah, why now?)

“It’s about the security of the population, not fighting down insurgent numbers,” British Gen. Gordon Messenger has said.

About 3,000 U.S. Marines are involved in the fight.

The advance notice given to residents will help avert civilian casualties, a problem that has hurt the military’s credibility among Afghans. They are also trying to get those Taliban who aren’t hard-core to turn in themselves and their weapons.

Reaching the battleground could be one of the biggest challenges for NATO and Afghan troops. It’s a tough terrain hard to cross with tanks.

The town of Marjah is surrounded by a deadly ring of roadside bombs, military officials say.

They say the Taliban has had months to plant bombs in the ground, most of them homemade mixes of ammonium nitrate, shrapnel fuel, salt or flour.

Such bombs have caused about 80 percent of the deaths in past fighting in Helmand province, military officials said. They are detonated remotely or by pressure plates.

“This is possibly the largest IED threat NATO has ever faced,” Nicholson has said.

Massive armored vehicles, called assault breacher vehicles, were to lead the charge into Marjah, coalition authorities said before the offensive.

The tank-like vehicles can destroy roadside bombs. Even with their help, though, military officials have increased staff at the hospital at Camp Bastion, in the capital of Helmand province, in anticipation that roadside bombs would cause casualties.

Troops also expect to encounter booby-trapped houses, as well as fierce urban combat.