No group has claimed responsibility for the blast yet, but Shia leaders blamed the attack on Lashkar-e-Jhangvi, the banned extremist Sunni Muslim group, which claimed the killing of over 200 Shia Muslims in two separate attacks in southwest city of Quetta over the last two months.
The recent attacks seemed to be retaliation for the arrest of Malik Ishaq, the current head of Lashkar-e-Jhangvi, last month in eastern Punjab province.
Sectarian violence is not unusual in Karachi where lots of people were gunned down in confrontation between Shia and Sunni Muslims, but massive bombing in a Shia community is quite rare in the city.