At least 44 people have been killed after a suspected suicide bomb detonated in northwestern Pakistan. 

Nearly 200 people have also been injured and 15 have been described as in a critical condition - meaning the death toll could rise further in the coming days.

The bomb went off at a political rally in the city of Khar to support the JUI-F, led by the hardline Islamist cleric Maulana Fazlur Rehman.

Mr Rehman himself was not in attendance at the rally.

"I was near the water dispenser to fetch a glass when the bomb exploded, throwing me to the ground," one witness said.

"We came to the meeting with enthusiasm but ended up at the hospital seeing crying wounded people."

Pakistani investigators inspect at the site of Sunday's suicide bomber attack. (AP Photo/Mohammad Sajjad)

The JUI-F forms part of Pakistan's governing coalition and Prime Minister Shehbaz Sharif described those behind the attack as targeting “those who speak for Islam, the Quran and Pakistan" and pledged they would face “real punishment”.

"The terrorists are enemies of Pakistan, we will eliminate them from the face of existence," Mr Sharif said in a statement.

The motive for the attack has not yet been officially established and no organisation has yet claimed responsibility.

Mr Rehman is considered pro-Taliban and the group offered its condolences to the bereaved and said they hoped for a "speedy recovery of the injured".

Elections will be held in Pakistan within 60 of the dissolution of the National Assembly, which is due on August 13th.

Main image: Injured people lie on the bed at a hospital after Sunday's suicide bomber attack. Picture by: Alamy.com