FORWARD OPERATING BASE JACKSON, Afghanistan (AP) -- The jarring blast near the American base sent up a cloud of smoke that drifted silently in the breeze. "Not good," a U.S. Marine said. Minutes later, vehicles raced through the gates with the wounded, three Marines and half a dozen Afghans.

Some lay bloodied on stretchers as medics worked on them. Soon, a pair of helicopters swept in and scooped up the injured, including a bomb sniffer dog, for delivery to a military hospital.

Word spread. A suicide bomber in a car packed with explosives had attacked security forces in the Sangin district center, next to the Marine battalion headquarters in an area of southern Afghanistan that has seen some of the war's hardest fighting. Three Afghan police and four civilians were killed.

Marines at Forward Operating Base Jackson called Thursday's attack part of a battle of perceptions with Taliban insurgents in a war triggered by the 9/11 attacks.

The Taliban, driven from power after sheltering Osama bin Laden, need to remind residents they are capable of inflicting damage on any opponent. The Marines must convince the Afghans that they have weakened the Taliban so much that they could never pose a threat - even as the U.S. and its allies transfer security responsibility to Afghan forces by the end of 2014.

The Taliban aim to push the Marines onto the defensive with high-profile bombings, forcing them to conduct fewer patrols and hole up in their bases in a sign that their own security is more important than that of the Afghans. U.S. forces, in turn, are trying to expand operations outward from population centers to keep insurgents away from civilians who will ultimately decide the fate of their nation.

By targeting the seat of local government Thursday, insurgents in Sangin apparently sought to show they can dictate the tempo of the conflict, despite heavy pressure since last year by successive Marine battalions. The U.S. military describes such acts as a sign of desperation by an enemy that has lost sway over communities it once controlled.

The challenge of breaking the Taliban grip is especially formidable in Sangin, which lies in the traditional Taliban stronghold of Helmand province. The district acts as a regional transit hub and is a conduit to a major dam that provides electricity.

Here, insurgents oversee opium-bearing harvests of poppy with the profits filling fill their war chests.

Sangin also has one of the highest concentrations of concealed bombs in Afghanistan. More than 100 British troops died there during several years of operations.

The Marines pushed aggressively into Sangin in larger numbers than the British had, forcing the Taliban onto the defensive, often at heavy cost. They tried to lend legitimacy to newly appointed Afghan officials by bankrolling bridge construction and other public works projects in their name.

Fighting ebbed during the Islamic holy month of Ramadan, which ended more than a week ago, and American troops are poised for any upswing.

"We're kind of waiting for what the next step is," said Lt. Col. Thomas Savage, commander of the 1st Battalion, 5th Marine Regiment, which occupies Jackson, a former British camp. "We've got enough of a lid on it that they're not going to be able to come back hard."

Savage spoke days before Thursday's bombing in a key town that has become relatively secure. There was a time when the Taliban's white flags ringed the Jackson base, the commander said, and insurgent snipers fired on Marines on the perimeter walls. Many Afghan civilians have since returned, and Marines patrolling in armored vehicles drive past merchants manning their kiosks.

After the explosion, Afghan soldiers at Jackson leaped into pickup trucks to collect the wounded. Back at a base clinic, they used a blanket to haul one injured Afghan whose eyes darted wildly. Other men lay inert. A U.S. medic turned one over to check his back for unseen wounds.

The shrapnel wounds of two Marines were described as minor. A third Marine lay on a stretcher with his eyes closed, his face pale, his trouser legs cut away to aid treatment. His life was not in danger.

One of the wounded was a dog used by U.S. Marines to detect crudely made but lethal bombs. His hindquarters were soaked in blood.

"This is Drak. Drak got hit as well," a servicemen said to three dog handlers who put a muzzle on the animal and hoisted him onto a stretcher. "He's got a puncture wound on his hip. I don't know if he's got anything under his tail, but he's dripping pretty bad."

The battle for Sangin, which has a population of about 100,000, plays out most days in a slower, more subtle fashion. The Marine battalion aims to unify a patchwork of tribes, some with long-standing rivalries, and empower Afghans who can represent fractured communities and may be targets for assassination.

"There are no cookie-cutter solutions here," said Marine Capt. Casey Brock of Charlie Company. As an example, Brock, of Bend, Oregon, cited his operational area. It encompasses a fertile belt along the Helmand river with a relatively stable tradition of landownership and, on the other side of a paved highway, an arid zone known as the "Fish Tank" where a fluctuating population leases land and has little to unite it.

Savage, a veteran of three tours in Iraq, said there were a "million little problems" in Sangin and that an overarching solution, such as the U.S.-backed marshaling of Sunni militias that turned against al-Qaida in Iraq, could not work in the territory under his command.

"You can't do what we did in Iraq," he said. "You don't get an entire bloc to flip."

He said Sangin's population was tilting toward the Marines, but acknowledged there are "fence-sitters" whose long-term loyalties are unclear. This summer, when President Barack Obama announced plans for a troop drawdown in Afghanistan, Savage cast U.S. policy in stark terms in his conversations with tribal leaders: Support coalition forces and allow stability to take root, or endure more combat, with all its devastating fallout, before the Americans leave.

Even the Taliban cells in Sangin appear to operate independently, often without signs of coordination. Marines say their leadership in neighboring Pakistan provides broad direction.

On patrol one day, Lance Cpl. Patrick Hawco of Tivoli, New York, described the conflict as a "small unit leader fight" where troops of lower rank make spur-of-the-moment decisions that, drawn together, have a wider impact on the course of the war. In the Marines' case, a decision to walk down one alleyway instead of another, or to stop for tea with a tribal elder, is a matter of instinct and experience.

At this time of year, the corn harvest is approaching. The stalks rise green and strong up to 12 feet, towering over the Marines as they zigzag on paths through the dense fields, their body armor soaked in sweat. Marines can't use their high-tech optics in the corn, but sometimes they move into it to set ambushes.

"We have to make sure the enemy fears the corn, and not the other way around," Brock said. In this battle of perceptions, he said, the goal is to sow doubt in the opponent.

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