Updated

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.