Islamic State (IS), the ultra hardline Sunni militant group that considers all Shi'ites to be apostates, claimed responsibility the attack in an online statement, Reuters reported.
The pilgrims were en route back to Iran from the Iraqi Shi'ite holy city of Kerbala, where they had commemorated Arbaeen, the 40th day of mourning for the killing of Imam Hussein, a grandson of the Prophet Mohammad, in the 7th century AD, the medical sources said.
The gas station has a restaurant in its premises that is popular with travelers. Five pilgrim buses were torched by the force of the blast from the explosives-laden truck, a police official said.
Islamic State has intensified attacks over the past month in areas out of its control in efforts to weaken a U.S.-backed military offensive launched on Oct. 17 to retake Mosul, the last major city under IS control in Iraq.