KARACHI, Pakistan -- The death toll from a devastating explosion that ripped through a crowded market in the southwestern city of Quetta on Saturday rose to 84 people, and Shiite leaders called for the arrest of the attackers, according to police and rescue officials.
The attack occurred in a neighborhood dominated by Hazaras, a Shiite ethnic minority that has suffered numerous attacks at the hands of Sunni death squads.
A previous attack on Jan. 10, when a Sunni group bombed a snooker hall in Quetta, killed almost 100 Hazaras, prompting domestic and international outrage.
The police said that Saturday's bomb was apparently set off by a remote-controlled device that was hidden inside a water supply truck. The explosion caused a building to collapse, damaged two neighboring structures and a left a crater that was 12 feet deep and 6 feet wide.
Mir Zubair Mehmood, the Quetta police chief, said that the bomb contained 800 to 1,000 kilograms (as much as 2,220 pounds) of explosives. Local hospitals declared an emergency, and rescue efforts were hampered by angry crowds at the bomb site, where distraught Hazaras prevented the police, reporters and rescuers from reaching the scene.
Prime Minister Raja Pervez Ashraf quickly condemned the attack, emphasizing the government's resolve to fight "such dastardly acts" and vowing to bring the perpetrators to justice.
But the seeming ease with which the bombers struck, just one month after a similar sectarian attack in the same city, underscored the inability of Pakistan's security forces to counter the threat from extremist groups as the country moves toward general elections that are expected to take place by mid-May.
After the January attack, Mr. Ashraf flew to Quetta, the capital of Baluchistan Province, to meet with Hazara families who protested in the streets for four days, sleeping beside the coffins of the bombing victims to protest the government's inaction.
That protest captured the sympathies of Pakistanis across the country, and helped galvanize political opinion against a growing problem of sectarian attacks on minority Shiites in Quetta and Karachi and in northwestern Pakistan.
Standing at the protest site, Mr. Ashraf announced that the government was dissolving the provincial government and handing control to the provincial governor -- a move that Hazaras had hoped would stop the bloodshed.
But Saturday's attack shows that extremists can still operate with impunity in Baluchistan, Pakistan's largest but most sparsely populated province.
Several conflicts are raging in Baluchistan, including sectarian attacks on Shiites; a nationalist insurgency; and ethnically motivated killings. It is also home to Afghan Taliban insurgents who carry out attacks in Afghanistan from the province.
The largest sectarian group, Lashkar-e-Jhangvi, is widely believed to be based in the town of Mastung, south of Quetta. Few of its members have been captured or arrested.
Abbas Kumaili, a prominent Shiite leader, speaking at a news conference in Karachi on Sunday afternoon, strongly condemned the inability of the government to curb the killing of Shiites.
"The situation is worsening as no action is being taken against banned militant groups," Mr. Kumaili said. "In fact, these banned militant groups have become more organized and active."
Mr. Kumaili said Shiite leaders resented the failure of mainstream political parties to strongly condemn extremist Sunni groups.
Human rights organizations accuse the powerful Pakistani military of tacit collusion with the sectarian groups, who have reportedly helped the military quell the nationalist insurgency.
The military vehemently denies those accusations and says its forces are overstretched in the region. After the January bombing, responsibility for security in Quetta was handed to the paramilitary Frontier Corps, which vowed to dismantle the sectarian groups.
This article originally appeared in The New York Times.