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Latest bomb blast blamed on Boko Haram kills 20 in northern Nigerian university town of Zaria

  • A blood splattered wall and broken window lay testament after a bomb blast in Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)

    A blood splattered wall and broken window lay testament after a bomb blast in Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)  (The Associated Press)

  • A man lays injured following a bomb blast,  receives treatment at a hospital in Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)

    A man lays injured following a bomb blast, receives treatment at a hospital in Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)  (The Associated Press)

  • Nigerian senator Shehu Sani from Kaduna state, second left, talk to an injured man after a bomb blast as he and others receive medical treatment at a hospital in  Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)

    Nigerian senator Shehu Sani from Kaduna state, second left, talk to an injured man after a bomb blast as he and others receive medical treatment at a hospital in Zaria, Nigeria, Tuesday, July 7, 2015. A bomb blast in Nigeria's northern university town of Zaria killed 25 people Tuesday including a 2-year-old toddler, the Kaduna state governor reported, Tuesday, the latest in a string of deadly bombing and shooting attacks attributed to the Boko Haram Islamic extremist group.(AP Photo)  (The Associated Press)

The state governor says a bomb blast in Nigeria's northern university town of Zaria has killed 20 people.

Gov. Nasir el-Rufai of Kaduna state is urging citizens to avoid crowded public places including mosques and churches as Islamic extremists Boko Haram extend the breadth and tempo of attacks that have killed some 300 people in a week.

El-Rufai used Twitter to report Tuesday's "terrorist bomb attack." Local media said the explosion occurred at the government headquarters as civil servants were assembling for a training course.

Nigeria's police force announced increased security around mosques and churches after Boko Haram bomb and shooting attacks Sunday killed more than 60 people in a mosque and posh Muslim restaurant in central Jos city and at an evangelical Christian church in northeastern Potiskum town.