The blast struck a gathering called by senior politicians of the Awami National Party (ANP) in the northwestern city of Peshawar ahead of the May 11 general elections.
The attack underscored the threat posed by insurgent violence ahead of the elections, which would mark the first transition in Pakistan between elected civilian governments.
“It was a suicide attack,” senior police official Shafqat Malik said.
A spokesman for the Pakistani Taliban, which has threatened to attack the ANP ahead of the vote, claimed responsibility for the blast.
A hospital official said doctors were treating some 50 people wounded in the explosion, including dozens who were in critical condition.
The ANP has its roots among ethnic Pashtuns in northwest Pakistan, but espouses secular values, putting it in direct confrontation with Islamist ideologies of Pakistan’s Taliban.
Police said that Ghulam Ahmad Bilour, a veteran politician and senior member of the ANP, was among the wounded.
Bilour, a former railways minister, offered a $100,000 reward in September for anyone who killed the makers of a film he said was insulting to Islam and that sparked protests in many Muslim countries. He invited the Taliban and al Qaeda to join him in what he called at the time a “blessed mission”.
In a separate attack in volatile northwest Pakistan, at least eight security personnel were killed when a suicide bomber rammed an explosives-laden car into a military truck travelling through North Waziristan, part of Pakistan’s tribal belt, intelligence officials said.
The officials said at least 12 people were wounded in the blast, a reminder of the potent threat posed by insurgents on the border with Afghanistan where militancy is rife.