A blast hit a Shiite Muslim religious procession killing 16 people and wounding 20 others in central Pakistan on Sunday, police said, amid conflicting reasons for the explosion.
It may have been a bomb or as a result of an electrical explosion, police said in Punjab province, but Shiites have often been targeted in Pakistan before.
Fingers were pointed at fanatics in Pakistan after an unprecedented bomb attack targeting Shiite Muslims on December 6 in neigbouring Afghanistan killed more than 80 people.
The twin blasts in Kabul and in the northern city of Mazar-i-Sharif prompted fears that Afghanistan could descend into the sort of sectarian violence that has pitched Shiite against Sunni Muslims in Iraq and Pakistan.
Sunday's explosion in Rahim Yar Khan district came as Shiites were marking the 40th day of mourning the death of the Prophet Mohammed's grandson Imam Hussain.
"The death toll has risen to 16, another 20 people have been injured," Mohammad Mushtaq, a senior government official, told the private Dunya TV channel.
The injured have been taken to local hospitals, he added.
"We are trying to calm the situation," Mushtaq said.
"We have evidences which shows that it was a bomb blast. We are also checking whether a suicide bomber was involved or not."
But Suhail Zafar, a senior police official, told the private Geo TV channel that police 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.
Shiites account for some 20 % of Pakistan's mostly Sunni Muslim population of 160 million.
More than 4,000 people have died in outbreaks of sectarian violence between the groups since the late 1980s.
On September 20, gunmen killed 26 Shiite pilgrims after ordering them off their bus in Mastung, a district 50 kilometres (30 miles) south of Quetta.
It was the deadliest attack on Shiites in Pakistan since September 4, 2010, when a suicide bomber killed at least 57 people at a rally, also in Quetta.
Gunmen then killed another three Shiites on the outskirts of the city who were going to collect relatives who died in the first incident.