Hundreds of Shias have joined a protest with the bodies of some of the 85 people killed in Saturday's attack at HazaraTown in Quetta, the capital of the restive Balochistan province.
The banned Lashkar-e-Jhangvi claimed responsibility for the bombing.
A bomb containing hundreds of kilograms of explosives ripped through a crowded market in HazaraTown on Saturday.
Many women and children were among the dead. About 200 people were injured by the blast, which flattened several buildings.
Leaders of the Shia Hazara community, which has been repeatedly targeted by sectarian groups like the LeJ, gave the government a 48-hour ultimatum to launch an army operation against terrorists.
They accused elements of the security establishment of sheltering the militants.
Quetta police chief Wazir Khan Nasir said officials were engaged in negotiations with the Shia leaders to convince them to bury their dead.
However, Shia leader Qayyum Changezi said the protesters would not bury the dead "until a targeted operation is launched" against terrorists.
Syed Muhammad Hadi, a spokesman for an alliance of Shia groups, said the community wanted security in Quetta to be handed over to the army and targeted operations against terrorists and their supporters.
The paramilitary Frontier Corps is responsible for security in Balochistan but Shias say it is unable to protect them.
After 92 people were killed in a twin suicide bombing in another Shia neighbourhood of Quetta last month, Shia Hazaras had refused to bury their dead till the federal government took steps to protect them.
Their protest triggered similar demonstrations in cities across Pakistan and Prime Minister Raja Pervez Ashraf was forced to dismiss the provincial government and impose governor’s rule in Balochistan.
Shia leaders said the security situation had not improved despite the imposition of governor’s rule.
Federal Religious Affairs Minister Khurshid Shah today said the latest attack on the Shias had highlighted the failure of intelligence agencies.
Protests against the bomb attack were organised in several cities, including Islamabad, Lahore, Jacobabad and Larkana. Markets were closed at some places and Shia groups organised rallies.
A strike was observed in Quetta yesterday at the call of the Hazara Democratic Party.
Image: Shi'ite Muslims in Lahore gather to protest against Saturday's bomb attack in Quetta
Photograph: Mohsin Raza/Reuters