A powerful bomb ripped through a rally by supporters of a hardline cleric and political leader in northwestern Pakistan on Sunday.

Initial reports suggested at least 35 people had been killed in the blast in Bajur district, which borders Afghanistan.

More than 100 were injured and the death toll was expected to rise, officials said.

Many of the wounded were taken to the city's main hospital, with some of the injuries described as critical.

A government administrator said the serious wounded people were being airlifted to provincial capital, Peshawar, for better care.

No one immediately claimed responsibility for the attack but the Islamic State group operates across the border in Afghanistan.

Police said the explosion struck a workers convention of the Jamiat Ulema Islam party of Maulana Fazlur Rehman.

The event was held on the outskirts of Khar, the capital of Bajur district.

Rehman is considered to be a pro-Taliban cleric and his political party is part of the coalition government in Islamabad.

Maulana Ziaullah, the local chief of Rehman's party, was among the dead.

Senator Abdur Rasheed and former lawmaker Maulana Jamaluddin were also present but escaped unhurt.

Party officials said Rehman was not in the rally.

Bajur had been a safe haven for Islamic militants until recent years when the military carried out operations to eliminate their presence.

But militants still strike often, attacking security forces and civilians.

Reactions in Afghanistan: 

The Islamic Emirate’s spokesman Zabiullah Mujahid also reacted to the blast, saying that the Islamic Emirate condemned the attack. 
“Such crimes are not justifiable,” Mujahid said.

Former President Hamid Karzai on Twitter condemned the attack and called it "inhuman and non-Islamic."