LONDON -- The death toll after an apparent suicide bombing in Pakistan has risen to 54, officials said on Monday.

No organization has yet taken responsibility for blast, which injured dozens of others when it rocked a political rally in the country's northwest, local officials said.

"Those responsible will be identified and punished," Prime Minister Shehbaz Sharif said in a statement in Urdu. "The Pakistani nation, law enforcement agencies and our protectors will never allow such cowardly tactics of the enemy to succeed."

Counter-terrorism officers who were investigating the blast said they suspected the Islamic State group may have been behind it, police said in a statement.

The event had been put on by one of the leading Islamic parties, the conservative Jamiat Ulema-e-Islam, in northwestern Pakistan's Khyber Pakhtunkhwa province.

Funerals were underway for the victims on Monday, the party said in a series of posts on social media. "Every eye was full of tears, every face was mournful," said one message, which was posted alongside a video of a swarm of people carrying and praying over caskets.

"May Allah accept the martyrdom of the martyrs and grant patience to their families and give complete healing to the injured," Maulana Fazl-ur-Rehman, the party's leader, said in a statement.

President Arif Alvi "expressed deep grief and sorrow over the loss of precious lives" in the blast, his office said in a statement.

Police had said on Sunday that at least 44 people were killed and more than 100 others were wounded.

ABC News' Joes Simonetti and Edward Szekeres contributed to this story.