Rising sectarian attacks threaten to further destabilize nuclear-armed Pakistan just as it faces intense international pressure to crack down on Islamist militants.
Friday´s explosion struck a 1,000-strong crowd streaming toward a graveyard in Dera Ismail Khan for the burial of Sher Zeman, a Shiite leader who was gunned down in the city the day before.
Ashiq Salim, a doctor at the main hospital in the city of Dera Ismail Khan, said 25 bodies had been brought there and that medics were scrambling to treat another 60 people who were wounded.
Police said people angered by the attack fired on officers rushing to the scene, where TV footage showed a bloodstained street littered with shoes and torn clothing.
An Associated Press reporter in the city heard the gunfire and said troops had arrived to help restore order.
There was no immediate claim of responsibility for the attack.
Relations between Pakistan´s strong Sunni majority and Shiite minority are under growing strain from a series of attacks attributed to sectarian extremists.
In the deadliest recent incident, a car bomb killed 29 people and wounded scores near a Shiite mosque in Peshawar in December. On February 5, a suicide bomber killed 24 at a Shiite mosque in a central city.
Much of the bloodshed has been in the northwest, where the Taliban have seized control of swaths of territory including the Swat Valley, where they have defied a yearlong army operation.
Troops and militants have been observing a cease-fire in Swat since Sunday, when authorities announced a deal to introduce Islamic law in the area if militants lay down their arms.
Richard Holbrooke, the new US envoy for Afghanistan and Pakistan, said Thursday that he had raised concern about the deal during a phone call with Pakistan´s president.
Holbrooke told CNN that President Barack Obama was worried "that this deal, which is portrayed in the press as a truce ... does not turn into a surrender."
He said President Asif Ali Zardari had assured him it wouldn´t.
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Associated Press writer Ishtiaq Mahsud in Dera Ismail Khan contributed to this report.
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