A blast hit a Shia Muslim religious procession on Sunday killing 13 people and wounding 20 others in central Pakistan, police said, amid conflicting reasons for the explosion.
The blast in Rahim Yar Khan district, in Punjab province, came as Shias were marking the 40th day of mourning the death of the Prophet Mohammed's grandson Imam Hussain.
"Thirteen people have been killed and 20 more injured," Suhail Zafar, a senior police official, told the private Geo TV channel.
The injured have been taken to local hospitals, he added.
Police said they were unclear what caused the blast.
"We are investigating about the nature of the blast but it is yet not clear," Zafar said, adding that police experts had collected some evidence to show it could be a bomb.
"We are examining those evidences," he said.
Abid Qadri, another senior police official in Rahim Yar Khan, said: "It was not an act of terrorism."
"A long flag in the procession struck the high transmission power wire and caused the explosion in the transformer," he told reporters.