At least 26 people were killed and 70 wounded on Sunday when a bomb ripped through a crowded bazaar in a mainly Shia area of Pakistan's northwestern tribal region, officials told Al Jazeera.
The explosion occurred at the Eidgah market in Parachinar, the capital of Kurram tribal district.
A doctor at the district headquarters hospital, where the wounded were taken, told AFP news agency that most of the injured were in "critical condition" and said the death toll could increase.
No one immediately claimed responsibility for the attack, but the region is known for sectarian clashes between Sunnis and Shia, who make up roughly 20 percent of Pakistan's population of 200 million.
Pakistan has been battling armed groups since 2004 which has claimed the lives of tens of thousands of civilians and security forces personnel.
Overall levels of violence have decreased this year after a nationwide military-led offensive against the groups across the country, blocking their sources of movement, communication and funding.
There has also been a crackdown on Sunni groups that target Shia.
In July, the leader of an anti-Shia group behind some of Pakistan's worst sectarian atrocities was killed in a shoot-out with police, along with 13 other fighters.
Source: Al Jazeera and agencies