The discovery in the northwestern town of Dera Ismail Khan comes amid a nationwide security alert following a wave of suicide attacks across the country in two weeks.

The devices, weighing between eight to ten kilos (17.6 to 22 pounds), were planted near a bus stop on the road towards the Waziristan tribal zone, a hub of al-Qaeda and Taliban militants, police said.

"The bombs were for terrorist activity and their timely discovery has foiled the plot," town police spokesman Malik Ramazan told AFP.

Pakistan has been rocked by a series of attacks in the last few weeks which have claimed more than 20 lives, including a January 29 suicide bombing in Dera Ismail Khan which killed a policeman.

Most of the attacks have been blamed on Taliban militants fighting President Pervez Musharraf's security forces in the Waziristan tribal belt.