A suicide bomber struck worshippers during prayers Friday at a mosque close to the Afghan border, killing 48 people in an attack one official said may have been aimed at anti-Taliban elders praying during the holy month of Ramadan.
Militants have frequently attacked tribesmen who have dared speak up -- or raise arms -- against them in the border region, where al-Qaida and the Pakistan Taliban have long held sway. Rifts between insurgent factions have also led to mass casualty attacks there.
Pakistan has lost more than 35,000 people in militant violence since 2007, with mosques, markets and hotels all targeted.
The attack was especially shocking because it came not only on Islam's holiest day of the week but also during its holiest month, when observant Muslims fast during the daytime and spend extra time in prayer and communal activities.
More than 300 people were at the mosque in Ghundi, a village in the Khyber tribal region, local administrator Iqbal Khan said.
"All the evidence we have gathered confirms that it is a suicide attack," said Fazal Khan, another local official.
The blast killed 48 people, according to Khalid Mumtaz, a local government official. At least 85 were wounded, Khan said.
A top provincial official said several elders of the Maddo Khel tribe who were in the mosque could have been the targets. He said the tribe had been campaigning against the militants in the area, with the backing of the government. He did not give his name because he was not authorized to speak to the media.
The attack was the deadliest since twin bombings in mid-June killed 40 people in Peshawar. That attack was believed to be part of a series of bombings staged by militants in retaliation for the U.S. killing of al-Qaida chief Osama bin Laden May 2 in Abbottabad.
U.S. Secretary of State Hillary Rodham Clinton condemned the bombing.
"The slaughter of worshippers as they gathered at a mosque for Ramadan's Friday prayers underscores the brutality of those who would target civilians during a time of celebration and reflection for Muslims throughout the world," she said.
Earlier Friday in South Waziristan, a pair of U.S. missiles hit a house, killing four suspected militants, said two Pakistani intelligence officials who spoke on condition of anonymity.
Since 2008, America has routinely fired missiles at militant targets in the northwest -- a tactic that has increasingly angered Pakistan's leaders as well its people.
Meanwhile, in the southern city of Karachi, gunmen ambushed a police bus carrying officers to a violence-wracked corner of the city, killing four officers and wounding 40 others, said local government minister Manzoor Wassan.
The ambush early today capped an outbreak of ethnic and political unrest in the country's commercial heart over the last four days that has killed 60 people.