The attack hit the main stage at a rally of Jamiat-e-Ulema Islam (JUI), a religious party believed to be sympathetic to the Afghan and Pakistan Taliban’s war against the United States and its allies.
Pakistani government official Javed Khan said the bomb in the Kurram tribal region wounded at least 50 people, while two party leaders who attended the event escaped unhurt, according to the Associated Press.
The Kurram region, near the Afghanistan border, is controlled by Taliban or Al Qaeda-linked groups and frequently suffers sectarian violence between Sunni and Shia Muslims, according to the BBC.
No group has claimed responsibility for the attack, which one official called a suicide bombing.
A JUI candidate from the region, Maulana Ainuddin Shakir, said the Taliban were likely not involved in the bombing.
"We have received no threats from Taliban, and we don't expect them to disrupt our election activity," Shakir told Pakistani Geo TV. The attack could have been the product of a tribal feud, he added.
GlobalPost's Mariya Karimjee noted from Karachi that the Taliban has not claimed responsibility and it's unlikely the attack was carried out by them. In the past, "they've been pretty clear that they're against democracy and elections, and have owned up to their attacks."
Since April, more than 70 people have died in suspected Taliban attacks targeting mostly moderate and secular political parties, which Reuters notes has stopped candidates from openly campaigning for the May 11 general elections.
If successful, the upcoming elections will mark the first time in Pakistan's history that a democratic vote has transferred power between civilian governments.