SANGJANI, Pakistan — Militants attacked dozens of trucks ferrying vehicles for Western troops in Afghanistan early Wednesday near the Pakistani capital, a bold assault that killed seven people and illustrated the vulnerability of a crucial U.S. supply line.

Militants and ordinary criminals have often attacked NATO and U.S. supply convoys over the past two years, but Wednesday's strike was the first so close to the well-protected capital, something likely to cause particular unease. Much of the fuel and supplies for Western troops in Afghanistan travels through Pakistan after arriving in the port city of Karachi.

An Associated Press photographer saw around 60 containers damaged at a truck depot on the main road leading to the border with Afghanistan, about six miles (10 kilometers) from Islamabad. Many carried military vehicles such as Humvees.

Charred shells of the trucks were jumbled together at the depot, and firefighters were dousing small blazes. The pungent smell of smoke gripped the air as officials surveyed the damage.

The U.S. Embassy in Islamabad said about 30 trucks contracted to transport supplies for NATO were damaged in the attack in Tarnol and the matter was under investigation by Pakistani authorities.

A group of around 15 suspected militants first opened fire with automatic weapons and grenades before torching the trucks, police officer Kalim Imam said.

Police official Shah Nawaz said Wednesday afternoon that seven people died. The victims' identities were not known, but they were believed to be Pakistanis employed as drivers or assistants. Seven people were also wounded.

The convoy attacks have added impetus to American efforts to open new supply lines into Afghanistan, but commanders say they have not affected operations there. Guns, bombs and ammunition are not believed to be transported in the trucks, thousands of which make the journey each week.

The attack near Islamabad followed clashes between the Pakistani military and insurgents in the northwest tribal belt bordering Afghanistan that killed 54 people, including eight soldiers, officials said.

One clash occurred in Orakzai tribal region when dozens of militants attacked a security convoy, sparking a battle that killed six soldiers and 40 militants, government administrator Samiullah Khan said. The army had declared Orakzai cleared of insurgents earlier this month.

Also Wednesday, government official Maqsood Khan said militants attacked two security checkpoints in Mohmand, another part of the tribal belt that has endured army operations. The overnight attack sparked gunbattles that killed two soldiers and six insurgents and wounded several from both sides.

Information from the tribal areas is nearly impossible to verify independently because they are remote and dangerous, and access is severely restricted.

Associated Press writers Habib Khan in Khar and Hussain Afzal in Parachinar contributed to this report.