Quetta anti-Shia bombing: Pakistan police detain '170'
Pakistani police say they have arrested 170 suspects after a bomb attack on Saturday which targeted a Shia Muslim area in the western city of Quetta.
Security sources said police killed four people, including a bomb-maker accused of anti-Shia attacks.
Saturday's bomb ripped through a busy market district, killing almost 90 people and injuring some 169 more.
Relatives of the dead are refusing to bury the bodies in protest at what they say is a lack of official action.
The authorities have previously been accused of turning a blind eye to the killing of members of the Shia minority.
In January bombers targeted a snooker hall in the city, killing some 90 people, sparking a similar protest by relatives of those killed.
Now both the security forces and the political leadership appear to be cracking down, the BBC's Orla Guerin reports from Islamabad.
Prime Minister Raja Pervez Ashraf has ordered an operation aimed at "eliminating those responsible for playing with innocent lives".
But some wonder if there will be sustained action against hard-line Sunni militant groups which were supported by Pakistan's intelligence agencies in the past, our correspondent reports.
Shia Muslim Hazaras are furious at what they see as a lack of protection from local and national forces, in the face of repeated attacks.
Sunni militant group Laskhar-e-Jhangvi said it had carried out the bombing, which hit a largely Hazara area of Quetta.
One local Shia leader, Qayyum Changezi, told AFP on Monday that the protesters would "not bury the dead until a targeted operation is launched".
It is not yet clear whether Tuesday's police action will be enough to persuade the community to end the protests.
Strikes and protests have been reported elsewhere in the country since the bombing, including in the commercial capital, Karachi.
Another bomb at a Shia mosque earlier in February killed 24 people, raising the Shia death toll to more than 200 in less than two months, according to reports.
On Sunday, Balochistan Governor Nawab Zulfikar Magsi - given greater powers after the recent blasts - said local security forces were either "too scared or too clueless" to act.
He said he had given security forces a "free hand" to take action against extremist groups, but that this had clearly failed.
"It's their job to pre-empt such attacks. That's what they are paid for," he said.
BBC Afghan's Imran Ali says the inaction has come as no surprise to the Hazara community, and frequent targeted killings and bomb explosions in Quetta mean many Hazaras are living in a state of fear.
Many are apprehensive to leave their homes and those who work in areas that are deemed dangerous are told by their employers to stay at home, our reporter adds.
Quetta is the capital of Balochistan province, which borders Iran and Afghanistan, and has been plagued by a separatist rebellion as well as sectarian violence.
Hundreds of Shia Hazaras in Quetta have been killed in attacks over the past few years.