(Adds drone attack, details)
KHYBER, Pakistan, Aug 19 (Reuters) - A suspected suicide bomber killed at least 26 people in a mosque during Friday prayers in Pakistan's northwestern tribal region of Khyber on the Afghan border, government officials and witnesses said.
More than 60 people were also wounded in the attack in Jamrud, the main town of Khyber, where militants have been active for the past several years.
"We have found ball-bearings at the blast site which indicate it could be a suicide attack," senior government official Khalid Mumtaz Kundi said.
Kundi said 20 bodies were brought to two hospitals, but relatives might have taken others directly to their homes.
Reports of casualties varied. Another official put the death toll at 26. A witness, Haji Zarmeen, said he helped removed at least 12 bodies from the rubble. A television channel said 40 people had been killed.
TV footages showed blood on the walls and ceiling of the mosque as people collected clothes and sandals scattered by the blast.
No one has claimed responsibility for the attack.
Pakistan has seen a wave of violence in recent years in which thousands of people have been killed.
There have been several bomb attacks since U.S. special forces killed al Qaeda chief Osama bin Laden in a secret raid in a Pakistani town in May.
Al Qaeda-linked militants have vowed to avenge bin Laden's death.
Pakistani troops have carried out several operations against the militants, but they have shown resilience and have responded with a campaign of suicide and bomb attacks across the country.
Since bin Laden's death, Washington has stepped up pressure on Pakistan to go after militants, using its border sanctuaries to attack U.S. forces in Afghanistan.
It has also intensified its campaign of drone attacks in Pakistan's northwest.
A U.S. drone fired two missiles at a house in the South Waziristan tribal region on the Afghan border, killing four suspected militants on Friday, local intelligence officials said.
Drone strikes have been a major source of friction between the United States and Pakistan. Ties have deteriorated since the death of bin Laden in the attacks which Pakistan sees as a violation of its sovereignty.
Pakistan's largest city and commercial hub Karachi also suffered from violence, with criminal, political and ethnic mayhem entering a third day. At least 55 people have been killed since Wednesday, police said.
Seven people were killed on Friday in violence that started as gang warfare, but has since expanded to include political and ethnic clashes -- a phenomenon that has long plagued the city of more than 18 million. (Additional reporting by Rebecca Conway; Writing by Augustine Anthony; Editing by Chris Allbritton and Miral Fahmy)
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