QUETTA, Pakistan: Thousands of Pakistani Shiite Muslims called off nationwide protests Tuesday and agreed to bury the dead from a bomb attack that killed 89 people, after the government promised to arrest those responsible.

Saturday's attack was the second bomb targeting the Shiite Hazara minority in five weeks in Quetta and saw protesters pour onto the streets across the country, shutting down parts of Karachi, Lahore and Islamabad.

Shiites, who make up around 20 percent of the mostly Sunni Muslim population of 180 million, are facing record numbers of attacks, raising serious questions about security as nuclear-armed Pakistan prepares to hold elections by mid-May.

Outlawed militant group Lashkar-e-Jhangvi (LJ) has claimed responsibility for the Quetta attacks and Shiites were furious that authorities have done nothing to prosecute those responsible.

Prime Minister Raja Pervez Ashraf sent cabinet ministers to the southwestern city to negotiate with the protesters and announced an operation to arrest those responsible for the attack.

Officials said security forces had killed four men and detained more than 170 alleged suspects, including the purported mastermind of Saturday's bombing.

Pakistani security forces frequently detain people en masse after major bombings but few if any are ever charged. In 2011 a court released the head of LJ Malik Ishaq on bail, even though he has been implicated in dozens of murders.

But a spokesman for the protesters announced alongside Information Minister Qamar Zaman Kaira after talks that the protest was over.

"The sit-in protest all over Pakistan is now finished and people should disperse peacefully," said Allama Amin Shahidi, from the Shiite Wahdatul Muslemeen party.

"The government has assured us that they will fulfil all our demands. The governor and the government told us that a targeted operation has begun, which will continue until all the culprits are eliminated."

The dead are now expected to be buried later on Tuesday or early on Wednesday.

Kaira promised the operation would "arrest all the culprits and eliminate them" and said a committee would be set up to oversee the protesters' demands for compensation, protection and jobs for families of the victims.

Since late Sunday, scores of coffins lay in neat rows, most decorated with pictures of the victims, in the the courtyard of a Shiite mosque near the protest site.

Relatives sat with the coffins reciting verses for the dead from the Koran. The youngest victim was a five-year-old boy who died along with his mother when the bomb, containing nearly a tonne of explosives, demolished a shopping centre.

Last month, Shiites called off a similar protest when Islamabad sacked the provincial government and imposed governor's rule after suicide bombers killed 92 people at a Hazara snooker hall in Quetta on January 10.

Quetta is a small town where the military and intelligence agencies have a heavy presence. Rights groups have questioned whether authorities are complicit with extremists or just incompetent.

Amnesty International repeated calls for Pakistan to do more to protect Hazaras, describing the failure to bring those responsible to justice as "shocking".

Attacks targeting Shiites in Pakistan have claimed almost 200 lives already this year. Human Rights Watch said more than 400 were killed in 2012, the deadliest on record for Shiites.

Hazaras have suffered disproportionately in Baluchistan, where authorities are also battling to suppress a separatist insurgency.