"Hundreds of tankers and trucks have been left stranded on highways and depots across Pakistan, with little or no security. Taliban militants have regularly been targeting the convoys, even when they are heavily protected. But many believe it is not just the militants who pose a security threat to the convoys. The owners of oil tankers being used to supply fuel to Nato in Afghanistan say some of the attacks on their convoys are suspicious. They say there is evidence to suggest that bombs have been planted in many of vehicles by the "Nato contractors" - individuals or companies who have been contracted by Nato to supply fuel and goods to forces in Afghanistan."