A suicide bomber has struck police escorting a protest rally in the eastern Pakistani city of Lahore, killing at least 13 people and wounding nearly 60 in an attack claimed by a breakaway Taliban faction.
The blast ripped through the crowd of hundreds of pharmacists, who were protesting over new amendments to a law governing drug sales.
Six police officers, including a former provincial counterterrorism chief, were among those killed, police said.
Police initially said the attacker was on a motorbike, but provincial law minister Rana Sanaullah later said that closed-circuit footage revealed the bomber was on foot.
Sameer Ahmad, the Lahore deputy commissioner, said at least 13 people were killed and 58 wounded, including nine who were in critical condition.
Live TV registered a loud bang and showed smoke and fire billowing up as people ran away, some of them carrying the wounded.
"We just couldn't understand what happened," Tufail Nabi told local Geo News TV.
"It was as if some big building collapsed," he said as he limped away.
A group called Jamaat-ul-Ahrar claimed the attack in a text message, saying it was revenge for Pakistani military operations against Islamic militants in tribal regions along the Afghan border.
The group, which claimed a number of large attacks last year, is one of several splinter factions from the Pakistani Taliban, which has repeatedly targeted security forces and religious minorities.
In recent years, Pakistan has launched several offensives against the Taliban and other Islamic militants in the tribal regions.
Prime Minister Nawaz Sharif vowed to continue fighting terrorism "until we liberate our people of this cancer and avenge those who have laid down their lives for us".
Elsewhere in Pakistan, a roadside bomb killed two members of a bomb disposal squad on the outskirts of the south-western city of Quetta, said police officer Abdur Razzaq Cheema.
Another eight people were wounded, he said.
A Taliban-linked group, Lashkar-e-Jhangvi, said it planted the bomb.