Bomber struck as hundreds gathered for meeting of Awami National Party.
The death toll climbed to 25 from a suicide bombing at a weekend election rally in northwest Pakistan, officials said, little over a week before key nationwide elections.
The bomber struck as hundreds of people gathered for a meeting of the Awami National Party (ANP), a small, nationalist ethnic Pashtun party, in the town of Charsadda in North West Frontier Province on Saturday.
Interior Minister Hamid Nawaz linked the attack to a wave of other bombings blamed on Al-Qaeda and Taliban militants that have claimed more than 70 lives this year.
"Twenty-five people have died and more than 35 are injured," provincial health minister Syed Kamal Shah told newswire AFP, although ANP leaders were not among the dead and wounded.
The government has formed an investigation team comprising senior police officials to probe the attack, he said.
Bomb disposal experts said that up to 10 kilograms of explosives mixed with metal pellets were used in the suicide bombing, which blasted big holes in two walls in the community centre hosting the meeting.
"Our estimate is that around eight to 10 kilograms of explosives were used in the suicide bombing and pellets caused most of the casualties," bomb disposal squad official Hukam Khan told AFP.
The bombing has further raised fears for the security of general elections on February 18, which have already been delayed by the assassination of opposition leader Benazir Bhutto at a rally in December.
The ANP announced a three-day mourning period and asked its workers to organise condolence meetings and hoist black flags at their offices, Mian Iftikhar Hussain, the party's provincial information secretary, told AFP.
"We have suspended the election campaign for three days and our workers shall hold condolence meetings to mourn the deaths," Hussain said.
Grief and anguish gripped the area as residents buried the dead. There were 24 funeral processions in the area on Sunday, residents said.
Moaning and crying relatives hugged each other while graves were dug in the rocky ground of several villages of the area, witnesses said.
An ANP leader addressing a press conference in Charsadda claimed that 30 supporters of his party were killed and more than 40 were injured.
Another party leader, Bashir Umarzai, said that the attack was "an attempt to assassinate the ANP leadership".
Last year, former interior minister Aftab Sherpao survived two suicide attacks in Charsadda that left dozens of people dead, the most recent in December.
Election rallies have been sparse since former premier Bhutto's death in a suicide bomb and gun attack in Rawalpindi on December 27 and after the government issued a "security advisory" for candidates to avoid big gatherings.
Meanwhile, two separate bomb blasts destroyed music and barber shops in Peshawar, the capital of the country's militancy-hit northwest, police said.
No one was injured by the improvised bombs, but the explosions damaged five shops late Saturday, local police officials said.
Nobody claimed responsibility for the blasts, but several music shops and hair salons have been attacked by pro-Taliban militants in the past who want to impose a strict Islamic code banning music and shaving of beards.