The blast targeted a van carrying police officers outside the Data Darbar shrine, the largest Sufi shrine in South Asia.
Lahore: The death toll in the suicide attack targeting one of Pakistan's oldest and most revered Sufi shrines in Lahore has risen to 13 as another civilian succumbed to his injuries, a media report said Monday.
Tahir Aslam, 18, was working at a shop near the shrine. He was among the critically injured and was brought to the Mayo Hospital where he has succumbed to his injuries.
He was rushed to the hospital after the blast which has claimed the lives of six policemen and seven civilians, the Dawn newspaper reported.
A senior police official told the daily on condition of anonymity that security forces had yet to make any substantial progress in the investigations into the attack.
He said that although they had arrested a few suspects from Lahore, they were no big leads.
A suicide bomber blew himself up outside the Data Darbar shrine, the largest Sufi shrine in South Asia on Wednesday, the second day of the the fasting month of Ramzan.
A CCTV footage showed a teenage boy wearing black shalwar kameez and a suicide vest coming closer to the vehicle of elite force beforing blowing himself up.
Punjab Inspector General of Police Arif Nawaz has said it was a suicide attack as the target was the vehicle of the elite force that was stationed outside the shrine of Sufi saint Ali Hajvari commonly known as Data Darbar. "Police was the target. 100 per cent," he said.
Lahore police spokesman Syed Mubashir has said the police have arrested four suspects with the help of CCTV cameras in the city.
The rickshaw used to transport the suicide bomber to the shrine has been identified, he added.
The CCTV footage shows the rickshaw driver approached the bomber as the latter emerged from Garhi Shahu area, some seven kilometres from the shrine.
Prime Minister Imran Khan condemned the attack and has directed the Punjab government to provide all assistance to the injured and families of victims.
Punjab Chief Minister Usman Buzdar has ordered an inquiry into the attack.
The famous shrine is visited by hundreds of thousands of people each year. In 2010, the heavily-guarded shrine was targeted in a suicide attack that killed more than 40 people.
Police also confirmed that Hizbul Ahrar had claimed responsibility for sending the teenage suicide bomber to the shrine.
The Counter Terrorism Department (CTD) of Punjab has examined the records of three terror groups, including the Ghazi Force and Jamaatul Ahrar.
Hizbul Ahrar is a splinter group of Jamaatul Ahrar headed by Muqarram Shah from Afghanistan. It separated from Jamaatul Ahrar due to internal rifts.
It started operating separately to target primarily the law enforcement agencies in various parts of Pakistan, the police said, adding the CTD is also following other leads, like the possibility of the involvement of Islamic State terror group.