Pakistan has seen a resurgence of attacks by Islamist militants since last year.
The casualties in a suicide bombing at a political rally held by a religious party rose to 45 on Monday, officials said, an attack compounding fears of unrest ahead of a general election due later in the year.
The bomber attacked the gathering of the conservative Jamiat Ulema Islam-Fazl (JUI-F) party, which is allied with the government and known for its links to hardline Islamists, in the Bajaur district on Sunday in the northwest, near the border with Afghanistan.
No group has claimed responsibility.
An official at a state-run rescue agency, Bilal Faizi, said the casualties had risen to 45. Of more than 130 wounded people, 61 were under treatment, said government health adviser Riaz Anwar.
A police counter-terrorism wing investigating the blast suspected the Islamic State group was behind it, police said in a statement.
Pakistan has seen a resurgence of attacks by Islamist militants since last year when a ceasefire between the Pakistani Taliban, the Tehreek-e-Taliban Pakistan (TTP), and the government broke down.
A mosque bombing in Peshawar city in the northwest killed more than 100 people in January but attacks on political parties are rare.
While the TTP and associated groups have been behind most of the attacks in recent months, the group distanced itself from Sunday's attack with a spokesman condemning it.
The JUI-F is an ally of the coalition government of Prime Minister Shehbaz Sharif who denounced the blast as an attack on the democratic process.
Prospects for the general election, due by November, have already been clouded by months of rivalry between main parties and accusations of military involvement in civilian politics. The military denies that.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)