Islamabad: Pakistani Shi'ites, targeted in three explosions which killed 16 people on Wednesday, are now receiving death threat text messages on cellphones ahead of a key event in their religious calendar that has been tainted by violence in the past.
"Kill, Kill, Shi'ites," say the text warnings to members of the minority sect.
Hardline Sunni militant groups linked to al Qaeda have in recent months stepped up attacks against Pakistan's Shi'ites, whom they regard as non-Muslims.
Pakistan's Taliban claimed responsibility for Wednesday's violence and said it would stage more attacks on Shi'ites over the next few days.
More than 300 Shi'ites have been killed in Pakistan so far this year in sectarian conflict, according to human rights groups.
"Genocide against Shi'ites is already taking place in Pakistan so the text messages don't really matter that much," said Jalal Haider, who received a text threat.
Hardline Sunnis are expected to strike again this weekend, the climax of the Shi'ite mourning month of Muharram. Radical Sunni groups have staged high-profile suicide bombings against processions on that occasion before.
Muharram marks the anniversary of the Battle of Karbala where the grandson of the Prophet Mohammad and his family members were killed.
About 50,000 people are expected to march through the streets of Islamabad on Saturday and thousands of security personnel are expected to be deployed in a bid to avoid attacks.
Any large-scale sectarian violence could hurt Pakistan's efforts to show it has improved security as it hosts the leaders of eight developing countries at a summit in Islamabad.
Pakistani intelligence officials say extremist groups, led by Lashkar-e-Jhangvi, or LeJ, have escalated their bombings and shootings of Shi'ites to trigger violence that would pave the way for a Sunni theocracy in US-allied Pakistan.
The schism between Sunnis and Shi'ites developed after the Prophet Muhammad died in 632 when his followers could not agree on a successor.
Sunnis recognise the first four caliphs as his rightful successors. The Shi'ites believe the prophet named his son-in-law Ali. Emotions over the issue are highly potent in modern times, pushing some countries, including Iraq five years ago, to the brink of civil war.
Pakistan is nowhere near that stage but officials worry that LeJ and other groups have succeeded in dramatically ratcheting up tensions and provoking revenge attacks in their bid to destabilise the nuclear-armed country.