The Shi'ite community in Pakistan is threatening to hold widespread protests if the government fails to arrest in 48 hours those responsible for the market bombing that killed 87 in Quetta, the regional capital of Balochistan province.
They also say they will postpone burying the dead from the February 16 attack.
Shi'ites in Quetta refused to bury victims of a similar attack in January that killed 86 people.
That bombing triggered days of protests that eventually toppled the local government.
Lashkar-e-Jhangvi, a banned Sunni group, said it was behind both attacks.
To protest the bombing, a general strike is planned in Karachi today, with schools and shops expected to close.
On February 17, UN Secretary-General Ban Ki-moon "strongly" condemned the attack, most of whose victims were ethnic Hazaras.
Many of the Shi'a in Quetta, including those in the neighborhood attacked on February 16, are Hazaras, an ethnic group that migrated to Pakistan from Afghanistan more than a century ago.
Based on reporting by Reuters and AP