Unknown gunmen today set three oil tankers, owned by Nato forces stationed in Afghanistan, ablaze in two separate attacks in the north western tribal region and the south western Baluchistan district, it was reported here. Police said the gunmen implanted a bomb in an oil tanker and set it ablaze while passing at the tribal village of Lendi on Khyber passage leading to Afghanistan, completely destroying it. The gunmen also attacked two Nato-owned oil tankers in Nasirabad District in Baluchistan and set them to fire.