NEAR MARJAH, Afghanistan  —  U.S. Marines and Taliban insurgents exchanged gunfire Thursday on the outskirts of Marjah, a southern militant stronghold where American and Afghan forces are expected to launch a major attack in the coming days.

To the north, a U.S.-Afghan force led by the U.S. Army's 5th Stryker Brigade linked up with Marines on Thursday, closing off a Taliban escape route to the nearby major city of Lashkar Gah.

Michael Yon reports from Afghanistan

No casualties were reported in the scattered clashes, which broke out as Marines moved ever closer to the edge of the farming community of 80,000 people, the linchpin of Taliban influence in the opium poppy producing province of Helmand.

Marines said the Taliban defenders were apparently trying to draw the Americans into a bigger fight before the U.S. was ready to launch the main attack.

"They're trying to draw us in," said Capt. Joshua Winfrey, 30, of Tulsa, Okla., commander of Lima Company, 3rd Battalion, 6th Marines.

Through much of the day, insurgents repeatedly fired rockets and mortars at the American and Afghan units poised in foxholes around the town, 380 miles southwest of Kabul.

"I am not surprised at all that this is taking place," said the battalion commander, Lt. Col. Brian Christmas. "We are touching their trigger-line," referring to the outer rim of the Taliban defenses.

U.S. commanders estimate they are facing between 400 and 1,000 Taliban fighters in the town, the largest in the south under militant control. Plans call for the joint U.S.-Afghan force to seize the town and quickly re-establish government control, offering services such as water, electricity and schooling to win the support of the local population.

U.S. officials have not disclosed how many Afghan and allied troops will take part in the battle but estimates range in the thousands. They also include British forces and U.S. soldiers from the 5th Strykers, which will intercept Taliban fighters trying to flee the town.

The major threat is expected to come from thousands of mines and roadside bombs, which the military calls improvised explosive devices, which the Taliban are believed to have planted in the area.

"This may be the largest IED threat and largest minefield that NATO has ever faced," said Brig. Gen. Larry Nicholson, commander of Marines in southern Afghanistan.

The U.S.-Afghan force led by the 5th Strykers found it slow going through the mines and roadside bombs as they pushed south toward Marjah, delaying their linkup with the Marines. When the Army force reached the rendezvous area, Marines popped violet-colored smoke grenades to mark their positions for the American soldiers.

Canadian advisers with the Afghan units set off yellow smoke so the Marines would know they were friendly forces.

Lt. Col. Burton Shields, commanding officer of the 4th Battalion, 23rd Infantry Regiment of the 5th Strykers, said the force had faced "harassing attacks" by groups of seven to nine insurgents.

"They're trying to buy time to move their leaders out of the area," he said.

NEAR MARJAH, Afghanistan  —  U.S. and Afghan forces pushed Tuesday to the edge of the southern Afghan town of Marjah, poised to seize the major Taliban supply and drug-smuggling stronghold in hopes of building public support by providing aid and services once the insurgents are gone.

Instead of keeping the offensive secret, Americans have been talking about it for weeks, expecting the Taliban would flee. But the militants appear to be digging in, apparently believing that even a losing fight would rally supporters and sabotage U.S. plans if the battle proves destructive.

No date for the main attack has been announced but all signs indicate it will come soon. It will be the first major offensive since President Barack Obama announced last December that he was sending 30,000 reinforcements to Afghanistan, and will serve as a significant test of the new U.S. strategy for turning back the Taliban.

About 400 U.S. troops from the Army's 5th Stryker Brigade and about 250 Afghan soldiers moved into positions northeast of Marjah before dawn Tuesday as U.S. Marines pushed to the outskirts of the town.

Automatic rifle fire rattled in the distance as the Marines dug in for the night with temperatures below freezing. The occasional thud of mortar shells and the sharp blast of rocket-propelled grenades fired by the Taliban pierced the air.

"They're trying to bait us, don't get sucked in," yelled a Marine sergeant, warning his troops not to venture closer to the town. In the distance, Marines could see farmers and nomads gathering their livestock at sunset, seemingly indifferent to the firing.

The U.S. goal is to take control quickly of the farming community, located in a vast, irrigated swath of land in Helmand province 380 miles southwest of Kabul. That would enable the Afghan government to re-establish a presence, bringing security, electricity, clean water and other public services to the estimated 80,000 inhabitants.

Over time, American commanders believe such services will undermine the appeal of the Taliban among their fellow Pashtuns, the largest ethnic group in the country and the base of the insurgents' support.

"The military operation is phase one," Helmand Gov. Gulab Mangal told reporters Tuesday in Kabul. "In addition to that, we will have development in place, justice, good governance, bringing job opportunities to the people."

Marjah will serve as the first trial for the new strategy implemented last year by the top U.S. commander in Afghanistan, Gen. Stanley McChrystal. He maintains that success in the eight-year conflict cannot be achieved by killing Taliban fighters, but rather by protecting civilians and winning over their support.

Many Afghan Pashtuns are believed to have turned to the Taliban, who were driven from power in the U.S.-led invasion of 2001, because of disgust over the ineffectual and corrupt government of President Hamid Karzai.

"The success of the operation will not be in the military phase," NATO's civilian chief in Afghanistan, Mark Sedwill, told reporters Tuesday. "It will be over the next weeks and months as the people ... feel the benefits of better governance, of economic opportunities and of operating under the legitimate authorities of Afghanistan."

To accomplish that, NATO needs to take the town without causing significant damage or civilian casualties. That would risk a public backlash among residents, many of whose sons and brothers are probably among the estimated 400 to 1,000 Taliban defenders. U.S. aircraft have been dropping leaflets over the town, urging militants not to resist and warning civilians to remain indoors.

Provincial officials believe about 164 families — or about 980 people — have left the town in recent weeks, although the real figure could be higher because many of them moved in with relatives and never registered with authorities.

Residents contacted by telephone in Marjah said the Taliban were preventing civilians from leaving, warning them they have placed bombs along the roads to stop the American attack. The militants may believe the Americans will restrain their fire if they know civilians are at risk.

Mohammad Hakim said he waited until the last minute to leave Marjah with his wife, nine sons, four daughters and grandchildren because he was worried about abandoning his cotton fields in a village on the edge of town. He decided to leave Tuesday, but Taliban fighters turned him back because they said the road was mined.

"All of the people are very scared," Hakim said by telephone. "Our village is like a ghost town. The people are staying in their homes."

Sedwill said NATO hopes that when Marjah has fallen, many Taliban militants could be persuaded to join a government-promoted reintegration process.

"The message to them is accept it," he said. "The message to the people of the area is, of course, keep your heads down, stay inside when the operation is going ahead."

Mangal, the governor, said authorities believe some local Taliban are ready to renounce Al Qaeda and give the government a chance.

"I'm confident that there are a number of Taliban members who will reconcile with us and who will be under the sovereignty of the Afghan government," he said.

Ali Ahmad Jalali, a former Afghan interior minister who lectures at the National Defense University in Washington, said the U.S. had little choice but to publicize the offensive so civilians could leave and minimize casualties. He said it would have been impossible to achieve complete surprise because "an operation of this scale cannot be kept secret."

But Jalali added that publicizing the operation may have encouraged hard-core Taliban to stand and fight to show their supporters and the international community that they will not be easily swayed by promises of amnesty and reintegration.

"Normally the Taliban would leave. They would not normally decisively engage in this kind of pitched battle. They would leave and come back because they have the time to come back," Jalali told The Associated Press.

"If there's stiff resistance in Marjah, this could increase the recruiting power of the Taliban or at least retain what they have in that area," he said. "It's become the symbol of Taliban resistance. So I would suspect it's possible there would be stiff rearguard resistance. If it becomes bloody, it would affect opinion in Europe and the U.S."

Jalali also said that success would depend on whether the Afghan government can make good on its promise of services once the battle is over.

"If the coalition can stabilize Marjah, rebuild it and install good governance, that can be an example for other places," he said. "If not, it would be another problem."

Echoing this theory, McChrystal told reporters at a defense conference in Turkey last weekend that it was necessary to tell Afghans that the attack on Marjah was coming so they would know "that when the government re-establishes security, they'll have choices."