Suspected Islamist militants torched more than 160 vehicles destined for US-led troops in Afghanistan yesterday in their biggest attack yet on the main military supply route through Pakistan.

The militants attacked the Portward Logistic Terminal in the northern city of Peshawar at around 2.30am, destroying its gate with a rocket-propelled grenade and shooting dead a guard, according to witnesses. They then set fire to about 100 vehicles, including 70 Humvees, which shipping documents showed were being shipped to the US-led coalition forces and the Afghan National Army.

Militants torched about 60 more vehicles at the nearby Faisal depot, which like Portward is on the ring road around Peshawar, where convoys typically stop before heading for the Khyber Pass.

Mohammad Rafiullah, a security guard at one of the terminals, said: “They were shouting ‘Allahu akbar' [God is greatest] and ‘Down with America'. They broke into the terminals after snatching our guns.”

The attackers fled after a brief exchange of fire with police, who arrived about 40 minutes later, witnesses said. It was the biggest in a series of militant attacks on Nato supply lines this year, which have raised fears that the Taleban are mimicking tactics used against British invaders in the 19th century and Soviet troops in the 1980s.

About 70 per cent of the fuel and other supplies for Nato and US forces in Afghanistan are shipped into the Pakistani port of Karachi and then driven over the Khyber Pass into Afghanistan. The rest are either driven from Karachi to southern Afghanistan through the Chaman border crossing or flown into Afghanistan. Nato and US officials insist their supply lines remain secure and flexible, but admit that they are looking for alternatives to the Khyber Pass following an increase in attacks on their convoys.

Last week suspected insurgents attacked another terminal near Peshawar and burned 12 trucks loaded with Nato supplies. Two guards were shot dead.

Last month the Government closed the Khyber Pass for a week after militants hijacked trucks and made off with supplies for US and Nato forces. Four US helicopter engines were stolen along the route in April and 36 Nato fuel trucks were torched near the pass in March.

The World Food Programme said it had also lost $320,000 (£217,000) worth of food aid in raids in northwestern Pakistan so far this year.

The US military in Afghanistan said in a statement that an unspecified number of its containers were destroyed in yesterday's attack, but that the losses would have “minimal effect on our operations”.

However, the US Defence Department is reported to have ordered an investigation into a possible alternative supply route through Europe, the Caucasus and Central Asia. Nato negotiated a deal with Moscow in April to open a new land route, but the plan has stalled since the war between Russia and Georgia.

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