Pakistani supply routes from the port of Karachi to land-locked Afghanistan are vital for Western forces battling the Taliban.

They are likely to be even more important as the US increases its troops in Afghanistan, perhaps doubling the number to about 60,000 this year.

Vulnerable supply chain

However, violence in the Khyber, such as the latest attack on Sunday, have forced Nato to look for alternative routes from central Asia into northern Afghanistan.

The other Pakistani supply route is through the border of Chaman, southwest of Khyber, to the southern Afghan city of Kandahar. But this route has also come under attack in recent times.

The US defence department says that it sends 75 per cent of its supplies into Afghanistan through or over Pakistan, including 40 per cent of the fuel for its troops.

But Taliban fighters have stepped up attacks on the main route through the Khyber Pass since last year, exposing the vulnerability of the supply chain.