A bomb struck at a political gathering Saturday in northwestern Pakistan, killing at least 25 people, wounding dozens more and stoking fears about security ahead this month's parliamentary election.

The Interior Ministry said the blast was due to bomber who blew himself up, but the mayor of Charsadda has said it was a planted bomb, according to a FOX News producer in Islamabad.

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In the south, an estimated 100,000 supporters of Benazir Bhutto turned out for her party's first major election rally since her assassination on Dec. 27. Bhutto's widowed husband told the crowd he had a responsibility to save the nation from President Pervez Musharraf's rule.

Also Saturday, riot police in the capital of Islamabad fired water cannons and tear gas at hundreds of lawyers protesting the detention of the deposed chief justice.

The violence underscored the deep tensions in Pakistan as the nation heads toward the Feb. 18 elections, which are meant to restore democracy after eight years of military rule. But campaigning has been overshadowed by Bhutto's killing, which U.S. and Pakistani officials blame on Islamic militants.

Saturday's blast occurred inside a hall where about 200 people had assembled for a political rally in the town of Charsadda, located in the turbulent North West Frontier province, where Islamic extremists have been battling government forces.

The rally was organized by the Awami National Party — a secular organization that competes against Islamist parties for support among the ethnic Pashtun community.

Abdul Waheed, 22, who suffered burns from the blast, said the bomb exploded as a member of the party was reciting verses from Islam's holy book, the Quran.

"I only heard the blast and cries and then something hit me and I fell down," Waheed told The Associated Press from his hospital bed in nearby Peshawar.

Television footage from the blast site, located in the sprawling residence of a party activist, showed the meeting hall littered with bloodstained clothes, shoes, police caps and overturned chairs. Policeman Mohammed Khan said two policemen were among the dead and several children had been killed or injured.

No group claimed responsibility for the attack, but suspicion fell on Islamic militants with ties to the Taliban and Al Qaeda. Interior Minister Hamid Nawaz said the militants are threatening all political parties in the northwest.

"They are against everyone," Nawaz told Dawn News TV.

Tensions have been running high across Pakistan since the charismatic Bhutto was killed in a homicide attack in Rawalpindi. Nowhere is the tension higher than in the North West Frontier province, a lawless region bordering Afghanistan where Islamic militants threaten government control.

Candidates have shied away from large outdoor rallies in favor of small gatherings of party stalwarts inside homes or high-walled compounds. Saturday's bombing showed that even those tightly controlled gatherings are unsafe.

Nevertheless, about 100,000 people gathered Saturday in a sports stadium in the southern city of Thatta as Bhutto's Pakistan People's Party resumed its election campaigning — suspended for the traditional 40 days of mourning after her death.

In an emotional speech, Bhutto's husband, Asif Ali Zardari, asked the crowd to "give me strength so that we can serve the country." He vowed to carry on his slain wife's mission.

"I have the responsibility to save Pakistan," Zardari said. "This is our country and we have to save it."

Zardari claimed his wife had been murdered by an establishment that she wanted to change.

"That is why they were against us," Zardari said. "If they try to stop me, I will destroy them and I hope you people will support me."

The government has rejected allegations that intelligence agents or members of the ruling party allied to Musharraf plotted to kill Bhutto.

Bhutto's party is widely expected to benefit from a sympathy vote. But it remains unclear whether Zardari can unite the party and dispel public doubts over allegations that he pilfered government funds and demanded kickbacks during Bhutto's two administrations in the late 1980s and 1990s.

Pir Bakhsh, a 24-year old laborer, said that Zardari's reputation was not good but that love for Bhutto "compels us to attend this rally."

"We will avenge the blood of Benazir. We don't have bombs. We are not terrorists, but we have political power and we will capitalize on this political power to avenge the death of Benazir," said Haji Jaffar, 75, a retired teacher. "The passion and love for (her party) has increased after Benazir's assassination."

Support for Musharraf plummeted when he launched a campaign last March against critics within the judiciary, including Chief Justice Iftikar Mohammed Chaudhry, who was fired three months ago and placed under house arrest.

About 1,500 lawyers tried to march Saturday to Chaudhry's barricaded home to protest his continued detention. When lawyers tried to breach the barbed-wire barricade, hundreds of riot police responded with tear gas, water cannons and a baton charge.

Several lawyers were roughed up, but there were no reports of serious injury.

Earlier Saturday, Pakistan's Bar Council announced that lawyers would boycott courts nationwide until the elections to pressure the government to restore Chaudhry and other senior judges.

Musharraf dismissed the chief justice and 60 other top judges after he declared emergency rule on Nov. 3, before the Supreme Court was to rule on the legality of his re-election as president. Musharraf lifted the emergency in mid-December, but Chaudhry, his wife and children remain under house arrest.