Three policemen were killed and several others injured in clashes with workers of the Tehreek-i-Labbaik Pakistan (TLP) Islamist party in Lahore, Dawn reported.
In a statement, Lahore DIG (Operation) spokesperson Mazhar Hussain identified two of the slain officials as Ayub and Khalid.
The identity of the third official has not yet been ascertained, but a statement from the provincial Chief Minister stated that three policemen were killed.
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Hussain said that several others were also injured and taken to the hospital in critical condition.
"Protesters also hurled petrol bombs on officials," he said, adding that officials tried to prevent them from vandalising and damaging public property.
"The angry mob also used sticks and pelted stones," he said, adding that officials were showing restraint despite the violence.
TLP media coordinator, Saddam Bukhari, said the police attacked the peaceful rally that was on its way to Islamabad, the Dawn report said.
In a separate statement, a spokesperson for the banned group in Pakistan said that workers had endured the "worst shelling in history" and were "attacked from all sides" near the Mao College Pul.
By late Friday night, the protesters had managed to reach Azadi Chowk, where they staged a sit-in for the night.
The group's leaders said they plan to leave for Islamabad at dawn.
The spokesperson claimed that at least 500 workers were seriously wounded while several had died.
However, as the violence erupted in Lahore, a statement issued by the proscribed group said that negotiations would not happen till TLP chief Saad Hussain Rizvi is released, the report added.
"They called us for talks, but attacked our workers from the back," a statement by the group's spokesperson said. He claimed that "thousands" were seriously injured and many had bullet injuries.
"Now, only the TLP chief will lead the negotiations," the spokesperson said.
The statement reiterated what the group had earlier demanded of the government.
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