Suspected Islamist militants in northern Pakistan have attacked a convoy carrying supplies to US and Nato forces in Afghanistan in the early hours of this morning, in the second such raid in as many days.

Witnesses and local officials said that several militants attacked a freight terminal on the outskirts of the city of Peshawar just after midnight, torching several dozen containers and military vehicles destined for Afghanistan.

"The militants came just past midnight, firing in the air, sprinkled petrol on containers and then set them on fire," said Mohammad Zaman, a security guard at the terminal on the Peshawar ring road.

"They told us they would not harm us, but they asked us not to work for the Americans," he said.

Some local officials said that about 50 containers were destroyed, while others said the attackers set nearly 100 vehicles alight including jeeps and 20 supply trucks.

Militants also fired rockets at two trucks carrying supplies for Nato forces as they drove along the ring road overnight, witnesses said.

Early yesterday, militants had attacked two other terminals, torching more than 160 vehicles destined for US-led troops in Afghanistan in their biggest attack yet on the main military supply route through Pakistan.

Witnesses to those attacks said that security guards were overrun by around 200 militants, who shouted "Allahu-Akbar" (God is Great) and "Down with America" as they broke into the terminals.

The raids are the boldest 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, often via airbases in the former Soviet Central Asian states of Uzbekistan and Kyrgyzstan.

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.

The Government last month 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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