More than two dozen militants had struck a terminal on the outskirts of Peshawar on Friday and planted devices on 12 out of 18 parked tankers carrying fuel for NATO troops in neighbouring Afghanistan.
Eleven tankers blew up while one remained safe. Militants also shot dead two guards drivers and two drivers who resisted them.
"An unexploded device in one of the 11 burnt tankers went off and triggered fire, which engulfed four tankers," local police official Imtiaz Shah told AFP.
He said that a bomb disposal squad rushed to the site and defused another unexploded timed device.
Another senior police official, Muhammad Ejaz confirmed the incident and said two persons in the terminal sustained minor injuries.
No group has so far claimed responsibility but the Taliban has claimed such attacks in the past. The bulk of supplies and equipment required by foreign troops in Afghanistan are shipped through Pakistan.
Pakistan shut its main northwestern border crossing to NATO supply vehicles for 11 days last September after a cross-border NATO helicopter assault killed two Pakistani soldiers.
Taliban and al Qaeda-linked militants frequently launch attacks across northwestern Pakistan and the lawless tribal belt on the Afghan border, which Washington has branded the most dangerous place in the world.
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