Their bus overturned on May 27 as it headed to a Shiite shrine.
Police say the bomb exploded as the bus was passing by the predominantly Sunni suburb of Saqlawiyah, located 75 kilometers west of Baghdad.
The bus was filled with Pakistani pilgrims who were headed from Syria to the gold-domed shrine to a Shi'ite imam in the northern Baghdad neighborhood of Kazimiyah.
Iraq is home to important Shi'ite holy shrines.
Pilgrims have been regular targets of bomb attacks by Al-Qaeda-linked groups.