Pakistani Shiites are demanding protection after a suicide bomber targeted an Ashoura procession on Friday night, killing at least 18 people and injuring 40 others.
Senior police officer Zafar Malik said the bomber detonated his device during a rally in Jacobabad, a city in the southern province of Sindh.
He said mourners are preparing for mass funerals and that the government has protectively deployed extra troops to handle any "untoward situation".
Minority Shiite Muslims hold public rallies to mark Ashoura, a 10-day ritual that commemorates the death of Imam Hussein, the grandson of the Prophet Muhammad and an iconic Shiite martyr.
Shiite community leader Syed Hamid Ali Shah Moosavi demanded protection on Saturday and asked the government to take action against those who orchestrated the bombing.