The bus was near the city of Peshawar when the bomb planted inside it exploded, almost completely destroying the back half of the colorfully decorated vehicle. The dead included six women, said senior police officer Tahir Ayub Khan. Another 35 people were wounded in the explosion, he said.
Jalal Khan, 14, was standing in the aisle of the crowded bus when the bomb went off and his right arm was slashed by a piece of metal.
"We all fell on the floor of the bus, and people were crying for help," said Khan, while receiving treatment at a local hospital. "I was unable to see anything because there was a lot smoke, and I was having trouble breathing."
Peshawar is located near Pakistan's semiautonomous tribal region, the main sanctuary for Taliban militants and their allies in the country. The city has suffered scores of bomb attacks over the past five years, but violence has fallen in recent months. The drop is partly due to Pakistani military operations against the Taliban in various parts of the tribal region.
Residents frantically shuttled bloodied victims from the bombing to the hospital in taxis, trucks and other private vehicles in the aftermath of the attack, local TV footage showed. Officials wheeled one woman into the hospital on a stretcher. She was covered by a blanket, and her clothes were soaked with blood.
Mohammed Javed, 35, was injured in the shoulder during the attack, but most of the blood soaked into his clothes came from other victims, he said.
"Luckily I was in the front part of the bus, and the bomb went off in the back," Javed said at the hospital. "Something hit me in the shoulder, but I kept my senses and started helping badly hurt people."
The bus departed from a government office in Peshawar and was headed for the nearby city of Charsada, said Javed. Both government employees and ordinary civilians normally used the bus, he said.
No group claimed responsibility for the attack, but the Pakistani Taliban have carried out hundreds of similar bombings across the country. The group is waging a bloody insurgency seeking to overthrow the government, partly because of its alliance with the United States. The Pakistani military has fought back but has had trouble clearing areas of the tribal region of militants, and they continue to strike back.
Iftikhar Hussain, the information minister for Khyber Pakhtunkhwa province, where Peshawar is the capital, said the government would relentlessly target the militants if they did not give up their fight.