The Pakistani Taliban have said they were behind Tuesday's attack on a Nato convoy near the capital, Islamabad.
The attack was carried out by tribal Mehsud fighters, spokesman Azam Tariq told the BBC Urdu service.
At least seven people were killed and several vehicles were set on fire in the assault which took place just 10km (six miles) from Islamabad.
Up to a dozen militants opened fire, setting 20 trucks alight and destroying millions of dollars of equipment.
The Nato trucks were carrying supplies to alliance troops in Afghanistan.
At least four people were injured in the attack. Most of the casualties were thought to be drivers of trucks or their assistants.
"Pakistani roads are being used to supply non-Muslim forces that are occupying Afghanistan," Tehrik-e Taliban Pakistan (TTP) spokesman Azam Tariq said.
"We will attack all traffic on these roads which we suspect of carrying supplies to those forces."
TTP has claimed responsibility for most attacks on Nato supply trucks in Pakistan in the past couple of years.
The trucks were attacked at around 2335 local time (1835 GMT) when they were parked at a roadside depot, police said.
They said that the attackers walked into the depot and started "indiscriminate firing".
They escaped in two cars and on motor-bikes to a nearby forest area.
Tuesday's attack is the most brazen to be carried out by militants in Islamabad, although since September 2008 Nato convoys have been regularly targeted in Balochistan and in the cities of Karachi and Peshawar.
The Taliban have hijacked lorries, stolen their cargo and kidnapped their drivers.
On one occasion in November 2008, militants captured Humvee armoured cars destined for Afghanistan and filmed themselves triumphantly driving off.
About 75% of the supplies needed by the 130,000 US-led international troops in Afghanistan are transported by land from the Pakistani port of Karachi.
But regular attacks have compelled Nato and American forces to look for other supply routes, principally through Central Asia.