On Saturday, a bomb tore through a busy market area killing at least 89 people - mostly Shia Muslims from the minority Hazara ethnic group.
A police operation launched after the attack has netted 170 suspects alleged to be linked to a series of bomb-blasts targeting Shias.
The arrests come as protests continue across Pakistan demanding authorities do more to stop sectarian violence.
Correspondent: Michael Edwards, South Asia Correspondent
Speakers: Hazara woman; Sajid Ishaq Sindhu, Chairman of the Pakistan Interfaith League; Imran Khan, politician
MICHAEL EDWARDS: Thousands of Hazara women are continuing their vigil in the centre of Quetta. They say they won't bury the dead from Saturday's blast until something is to stop the attacks on their community.
HAZARA WOMAN: Our request is here that we want army, army should come here and (inaudible).
MICHAEL EDWARDS: Saturday's attack was the second massive blast that targeted the Hazaras in Quetta this year.
In January more than a hundred people were killed when twin blasts destroyed a snooker hall.
The Sunni militant group - Lashkar-e-Janghvi - has claimed responsibility for both attacks.
And the anger felt by the Hazara community is shared across Pakistan. In the capital Islamabad, human rights activists as well as representatives from all Pakistan's religious communities lit candles for the victims.
The chairman of the Pakistan Interfaith League, Sajid Ishaq Sindhu, says all Pakistanis need to stand together to defeat extremism.
SAJID ISHAQ SINDHU: Today we are not gathered on the basis of religion, but we are gathered on the basis of humanity because we believe that we are all human beings first, and then we are Muslims, Christians, Hindu and whatever. And today we have Christians, we have bishops here, we have pastors, we have Muslim friends here, we have Hindus and Sikhs. It is a symbol of our unity. It's a symbol that people of Pakistan belong to one family.
MICHAEL EDWARDS: The Pakistani government is accused of turning a blind eye to the activities of militant groups such as Lashkar-e-Janghvi. But with pressure mounting on them to act, the police have conducted a sweep of people with known links to the group.
One hundred and seventy suspects have been arrested. Four were killed in a shoot-out with police.
Pakistan's cricket legend-turned-politician Imran Khan called a press conference to vent his anger at the group.
IMRAN KHAN (translated): I tell you by name, Lashkar-e-Janghvi, I tell you by name that this terrorism that you are carrying out in the name of Islam, there can be no bigger enemy of Islam than you.
Islam is the name of humanity. What you are doing to a different sect of your own religion is something you should not be doing to atheists. I strongly condemn you. I also strongly condemn you on behalf of the Pakistani nation. And I say that this terrorism, that through this that you are carrying out, you are harming Islam, you are harming Pakistan.
MICHAEL EDWARDS: Lashkar-e-Janghvi has stepped up suicide bombings and shootings on Shia Muslims in a bid to destabilise Pakistan and install a Sunni theocracy.
Experts say it's a strategy similar to that used by Al Qaeda to try to trigger a civil war in Iraq several years ago.