A bomb blast targeting a busy shopping district in Lahore killed at least two people, including a child, 9, and wounded 22 others on Thursday, Pakistani police and officials said.
A spokesman for the Baloch Nationalist Army, one of several ethnic separatist groups waging an insurgency for years in south-west Pakistan, claimed responsibility for the attack in a Twitter post.
"Initial investigations show that it was a time-controlled device on a motorbike which was the cause of the blast," Rana Arif, spokesman for Lahore police, told AFP.
The explosion took place in old Lahore's busy Anarkali shopping district, damaging several motorbikes and upturning market stalls.
Pakistani Prime Minister Imran Khan expressed regret over the "loss of precious human lives", a spokesman for his office said.
A spokesman for the Baloch Nationalist Army said it was responsible. "This attack targeted bank employees. A detailed statement will be issued soon," he said.
The mineral-rich region of Balochistan, bordering Afghanistan and Iran, is the largest of Pakistan's four provinces, but its roughly seven million inhabitants have long complained they do not receive a fair share of its gas and mineral wealth.
China is investing in the area under a $54 billion project known as the China-Pakistan Economic Corridor (CPEC), upgrading infrastructure, power and transport links between its far-western Xinjiang region and Pakistan's Gwadar port.
Baloch separatists have previously claimed responsibility for several attacks on CPEC projects, and thousands of Pakistani security personnel are stationed in the region to counter the violence.
Pakistan has suffered a string of blasts and attacks on police since December, when a truce between the government and Pakistan's Taliban lapsed.
Tehreek-e-Taliban Pakistan (TTP) – a home-grown movement that shares common roots with the Afghan Taliban – has claimed responsibility for most recent attacks.
The TTP said this week it was responsible for a deadly shoot-out in Islamabad on Monday night – a rare attack by the militants in the heavily guarded capital.
A police officer was killed and two others injured when two TTP gunmen opened fire on a police checkpoint from a motorbike.
Police said both attackers were killed and Pakistan's Interior Ministry gave a warning of the potential for further violence.
Pakistan's government announced late last year it had entered a month-long truce with the TTP, facilitated by Afghanistan's Taliban, but that expired on December 9 after peace talks failed to make progress.
The TTP has been blamed for hundreds of suicide bomb attacks and kidnappings across the country and for a while held sway over large tracts of the nation's rugged tribal belt, imposing a radical version of Sharia.
But after the massacre in 2014 of nearly 150 children at a Peshawar school, the Pakistan military sent vast numbers of troops into TTP strongholds and crushed the movement, forcing its fighters to retreat to Afghanistan.