Jamaat-ur-Ahrar, a faction of the Pakistani Taliban, claimed responsibility for the attack near Punjab's provincial assembly that left 13 dead and 89 others wounded on Monday.
Pakistanis on Tuesday mourned the deaths of at least 13 people who were killed in a Taliban-claimed suicide attack during a protest in Lahore, Pakistan's second largest city.
Eighty-nine people were wounded in the attack on Monday that targeted a protest organised by Pakistan's chemists and pharmaceutical manufacturers.
Shahbaz Sharif, chief minister of the central Punjab province, declared a day of mourning after the blast on Lahore's Mall Road, one of the city's main arteries, at rush hour.
TRT World spoke to Lahore-based journalist Hamza Ameer for more details.
Mushtaq Sukhera, inspector general of police in Punjab province, said five police officers were among the dead.
"It was a suicide attack. The bomber exploded himself when successful negotiations were underway between police officials and the protesters," Sukhera told reporters.
A spokesman for Jamaat-ur-Ahrar, a faction of the Tehreek-i-Taliban Pakistan (TTP), claimed responsibility for the attack.
The militant group also warned the Lahore attack was the start of a new campaign against government departments. "You are on our target across the country," it added in a statement.
The attack underscored the challenges faced by Pakistan in its push to stamp out militancy, even as security dramatically improved in 2015 and 2016.
Lahore residents vented their fury at the militants and the government at the blast site early Tuesday.
Blast in Quetta leaves two dead
Two members of a bomb disposal team were killed in Quetta, the capital of the restive Balochistan province, while trying to defuse a device, shortly after the Lahore blast on Monday.
The commander of the city's bomb disposal unit and a colleague were killed while trying to defuse an explosive device, police said.
"They died on the spot, their bodies blown up," Abdul Razzaq Cheema, deputy inspector general of police in Quetta, said of the two officers.
The militant group Lashkar-e-Jhangvi's Al Alami faction claimed responsibility on Tuesday.