Parachinar has a large Shiite population, unusual in Sunni-majority Pakistan, and locals have expressed fears that militias who splintered from the Taliban and sworn allegiance to so-called "Islamic State"( ISIS , ISIL , Daesh) might target them.
Pakistan also has its own sectarian militant groups, most notably Lashkar-e-Jhangvi (LeJ). Most of LeJ's leadership were shot dead in police custody this year; police say they were trying to escape.
No group has yet claimed responsibility for Sunday's blast.
Parachinar local government official Riaz Hussain said the blast targeted crowds at a market.
Some hours after massive blast Amjad Ali Khan, the political head of Kurram Agency, said a blast in Eid Gah market in Parachinar had killed 10 people including a child and wounded at least 50 others.
Parachinar is the capital of Kurram. Shafiq Hussain, a health worker at the Agency Headquarters Hospital Parachinar, said some of the injured were in critical condition and they were planning to send them to Peshawar and Kohat for better treatment.
Some of the people suffered injuries due to a stampede after explosion, he said.
"The death toll has reached 23 as many of the critically wounded succumbed to injuries as they were being shifted to helicopters to fly them to Peshawar," Amjad Ali Khan, the political administrator of Kurram, told AFP.